Stylus with customizable appearance

ABSTRACT

A stylus comprising: an elongate chassis molding; a nib at one end of the chassis molding; and, an elongate cover molding for close-fitting engagement with the chassis molding; such that, the cover molding is user replaceable.

FIELD OF THE INVENTION

The present invention relates to the fields of interactive paper,printing systems, computer publishing, computer applications,information appliances, human-computer interfaces, and in particularelectronic styli.

CO-PENDING REFERENCES

NPS101US NPS109US NPS110US

CROSS-REFERENCES

10/815621 10/815612 10/815630 10/815637 10/815638 10/815640 10/81564210/815643 10/815644 10/815618 10/815639 10/815635 10/815647 10/81563410/815632 10/815631 10/815648 10/815641 10/815645 10/815646 10/81561710/815620 10/815615 10/815613 10/815633 10/815619 10/815616 10/81561410/815636 10/815649 11/041650 11/041651 11/041652 11/041649 11/04161011/041609 11/041626 11/041627 11/041624 11/041625 11/041556 11/04158011/041723 11/041698 11/041648 10/815609 10/815627 10/815626 10/81561010/815611 10/815623 10/815622 10/815629 10/815625 10/815624 10/81562810/913375 10/913373 10/913374 10/913372 10/913377 10/913378 10/91338010/913379 10/913376 10/913381 10/986402 IRB013US 11/172815 11/17281410/409876 10/409848 10/409845 11/084769 11/084742 11/084806 09/57519709/575195 09/575159 09/575132 09/575123 6825945 09/575130 09/5751656813039 09/693415 09/575118 6824044 09/608970 09/575131 09/5751166816274 09/575139 09/575186 6681045 6678499 6679420 09/663599 09/6078526728000 09/693219 09/575145 09/607656 6813558 6766942 09/69351509/663701 09/575192 6720985 09/609303 6922779 09/609596 684788309/693647 09/721895 09/721894 09/607843 09/693690 09/607605 09/60817809/609553 09/609233 09/609149 09/608022 09/575181 09/722174 09/72189610/291522 6718061 10/291523 10/291471 10/291470 6825956 10/29148110/291509 10/291825 10/291519 10/291575 10/291557 6862105 10/29155810/291587 10/291818 10/291576 6829387 6714678 6644545 6609653 665187910/291555 10/291510 10/291592 10/291542 10/291820 10/291516 686788010/291487 10/291520 10/291521 10/291556 10/291821 10/291525 10/29158610/291822 10/291524 10/291553 6850931 6865570 6847961 10/68552310/685583 10/685455 10/685584 10/757600 10/804034 10/793933 688989610/831232 10/884882 10/943875 10/943938 10/943874 10/943872 10/94404410/943942 10/944043 10/949293 10/943877 10/965913 10/954170 10/98177310/981626 10/981616 10/981627 10/974730 10/986337 10/992713 11/00653611/020256 11/020106 11/020260 11/020321 11/020319 11/026045 11/05969611/051032 11/059674 NPA19NUS 11/107944 11/107941 11/082940 11/08281511/082827 11/082829 11/082956 11/083012 11/124256 11/123136 11/15467611/159196 NPA225US 09/575193 09/575156 09/609232 09/607844 645788309/693593 10/743671 11/033379 09/928055 09/927684 09/928108 09/92768509/927809 09/575183 6789194 09/575150 6789191 10/900129 10/90012710/913328 10/913350 10/982975 10/983029 6644642 6502614 6622999 66693856827116 10/933285 10/949307 6549935 NPN004US 09/575187 6727996 65918846439706 6760119 09/575198 09/722148 09/722146 6826547 6290349 64281556785016 6831682 6741871 09/722171 09/721858 09/722142 6840606 10/20202110/291724 10/291512 10/291554 10/659027 10/659026 10/831242 10/88488510/884883 10/901154 10/932044 10/962412 10/962510 10/962552 10/96573310/965933 10/974742 10/982974 10/983018 10/986375 11/107817 11/14823811/149160 09/693301 6870966 6822639 6474888 6627870 6724374 678898209/722141 6788293 09/722147 6737591 09/722172 09/693514 679216509/722088 6795593 10/291823 6768821 10/291366 10/291503 679789510/274817 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10/29154610/917355 10/913340 10/940668 11/020160 11/039897 11/074800 NPX044US11/075917 11/102698 11/102843 6593166 10/428823 10/849931 11/1448076454482 6808330 6527365 6474773 6550997 10/181496 10/274119 10/30918510/309066 10/949288 10/962400 10/969121 UP21US UP23US 09/517539 656685809/112762 6331946 6246970 6442525 09/517384 09/505951 6374354 09/5176086816968 6757832 6334190 6745331 09/517541 10/203559 10/203560 10/20356410/636263 10/636283 10/866608 10/902889 10/902833 10/940653 10/94285810/727181 10/727162 10/727163 10/727245 10/727204 10/727233 10/72728010/727157 10/727178 10/727210 10/727257 10/727238 10/727251 10/72715910/727180 10/727179 10/727192 10/727274 10/727164 10/727161 10/72719810/727158 10/754536 10/754938 10/727227 10/727160 10/934720 10/2965226795215 10/296535 09/575109 6805419 6859289 09/607985 6398332 63945736622923 6747760 6921144 10/884881 10/943941 10/949294 11/03986611/123011 11/123010 11/144769 11/148237 10/922846 10/922845 10/85452110/854522 10/854488 10/854487 10/854503 10/854504 10/854509 10/85451010/854496 10/854497 10/854495 10/854498 10/854511 10/854512 10/85452510/854526 10/854516 10/854508 10/854507 10/854515 10/854506 10/85450510/854493 10/854494 10/854489 10/854490 10/854492 10/854491 10/85452810/854523 10/854527 10/854524 10/854520 10/854514 10/854519 10/85451310/854499 10/854501 10/854500 10/854502 10/854518 10/854517 10/93462811/003786 11/003354 11/003616 11/003418 11/003334 11/003600 11/00340411/003419 11/003700 11/003601 11/003618 11/003615 11/003337 11/00369811/003420 11/003682 11/003699 11/071473 11/003463 11/003701 11/00368311/003614 11/003702 11/003684 11/003619 11/003617 10/760254 10/76021010/760202 10/760197 10/760198 10/760249 10/760263 10/760196 10/76024710/760223 10/760264 10/760244 10/760245 10/760222 10/760248 10/76023610/760192 10/760203 10/760204 10/760205 10/760206 10/760267 10/76027010/760259 10/760271 10/760275 10/760274 10/760268 10/760184 10/76019510/760186 10/760261 10/760258 11/014764 11/014763 11/014748 11/01474711/014761 11/014760 11/014757 11/014714 11/014713 11/014762 11/01472411/014723 11/014756 11/014736 11/014759 11/014758 11/014725 11/01473911/014738 11/014737 11/014726 11/014745 11/014712 11/014715 11/01475111/014735 11/014734 11/014719 11/014750 11/014749 11/014746 11/01476911/014729 11/014743 11/014733 11/014754 11/014755 11/014765 11/01476611/014740 11/014720 11/014753 11/014752 11/014744 11/014741 11/01476811/014767 11/014718 11/014717 11/014716 11/014732 11/014742 11/09726811/097185 11/097184 10/728804 10/728952 10/728806 10/728834 10/72979010/728884 10/728970 10/728784 10/728783 10/728925 10/728842 10/72880310/728780 10/728779 10/773189 10/773204 10/773198 10/773199 683031810/773201 10/773191 10/773183 10/773195 10/773196 10/773186 10/77320010/773185 10/773192 10/773197 10/773203 10/773187 10/773202 10/77318810/773194 10/773193 10/773184 11/008118 11/060751 11/060805 MTB40US11/097308 11/097309 11/097335 11/097299 11/097310 11/097213 11/09721210/760272 10/760273 10/760187 10/760182 10/760188 10/760218 10/76021710/760216 10/760233 10/760246 10/760212 10/760243 10/760201 10/76018510/760253 10/760255 10/760209 10/760208 10/760194 10/760238 10/76023410/760235 10/760183 10/760189 10/760262 10/760232 10/760231 10/76020010/760190 10/760191 10/760227 10/760207 10/760181 10/407212 10/40720710/683064 10/683041 6750901 6476863 6788336 6623101 6406129 65059166457809 6550895 6457812 10/296434 6428133 6746105

The disclosures of these co-pending applications are incorporated hereinby cross-reference. Some applications are temporarily identified bytheir docket number. This will be replaced by the corresponding USSNwhen available.

BACKGROUND OF THE INVENTION

The Applicant has developed the Netpage system discussed in detail belowand in many of the above cross reference documents. As the invention isparticularly well suited to this system, it will be described in aNetpage context. However, it will be appreciated that hand-held opticalsensors have broad ranging application in many different fields and theinvention is not limited to its use within the Netpage system.

This Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface).

Netpage pens have a unique identity so that the owner of the pen can berecorded in the network. Registering the owner of each pen has a numberof advantages such ‘walk-up’ printing (described in the co-pendingapplication Docket No. NPS110), signature recognition and so on. Inlight of this, pen owners will want to be able to quickly identify theirown Netpage pen(s) from those of others.

Beyond the Netpage context, most people with quality pens consider themto be personal property and may engrave them to indicate ownership.However, this has little impact on the appearance of the pen and thereis still a risk of confusion if several co-workers have the same brandof pen.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides a styluscomprising:

-   -   an elongate chassis molding;    -   a nib at one end of the chassis molding; and,    -   an elongate cover molding for close-fitting engagement with the        chassis molding; such that,    -   the cover molding is user replaceable.

By providing a cover molding that the user can easily remove and replaceat will, each pen can be individually customized. The owner of each pencan quickly distinguish their pen from those of others. Regularreplacement of the cover prevents the pen from looking worn and lets auser choose a new appearance if they tire of the old one, or if theydiscover a co-worker already has the same cover.

Optionally, the stylus is an electronic stylus wherein the chassismolding houses electronic components. Optionally, the cover molding is atubular molding that snap locks onto the chassis molding exterior.Optionally, the tubular molding is slid into place on the chassismolding, wherein the chassis molding has a location detail to indicatethat the tubular molding has been pushed home. Optionally, the tubularmolding can be slid off the chassis molding by grasping the nib end ofthe stylus and pulling the tubular molding off the opposing end.Optionally, the cover molding is a suitable substrate for aquagraphicprints.

Optionally, the chassis has LEDs to indicate the operational status ofthe stylus and the tubular molding has one or more transparent windowsfor viewing the LEDs.

Additional Aspects

Related aspects of the invention are set out below together with adiscussion of their backgrounds to provide suitable context for thebroad descriptions of these aspects.

Electronic Stylus with Substantially Triangular Cross-Section

Background

The Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface).

The pen is intended to be held in the same manner as a normal pen andtherefore inclined relative to paper instead of normal to the plane ofthe paper. The optical sensor is adjacent the nib and so the distancebetween the lens and the surface of the page will differ depending onwhether the lens is above, below or beside the nib as it is heldinclined to the paper. As the focal length of the lens is generallyfixed, the optics require a large depth of field and blur tolerance toaccommodate every possible position of the lens relative to the paper.This imposes practical limits on the size of the coded data, the opticsand the tilt of the pen during use.

Summary

Accordingly, this aspect provides a hand-held, electronic stylus for usewith a surface having coded data disposed thereon, the styluscomprising:

-   -   an elongate casing with a grip having a substantially triangular        cross section for pen-like manipulation of the stylus;    -   a nib at one end of the casing for contact with the surface, the        nib having a longitudinal axis that is offset from the        longitudinal axis of the casing; and,    -   a sensor positioned adjacent the nib for optically sensing the        coded data; wherein during use,    -   the stylus is held such that the longitudinal axis of the nib is        proximate the apex of the substantially triangular cross        section.

A rounded triangular profile gives the pen an ergonomically comfortableshape to grip and use the pen in the correct functional orientation. Itoffers a natural conformity to a triangular shape between thumb, indexfinger and middle finger. The range of pitch angles over which the penis able to image the pattern on the paper can be optimised for thisasymmetric usage. The shape of the pen helps to orient the pen correctlyin the user's hand and to discourage the user from using the pen“upside-down”.

It is also a practical shape for accommodating the internal components.The ballpoint pen cartridge fits naturally into the apex of thetriangular cross section, placing it consistently with the user's grip.This in turn provides space for the main PCB in the centre of the penand for the battery in the base of the pen. It also naturally places thetag-sensing optics unobtrusively below the nib (with respect to nominalpitch).

Optionally, the nib is a ball point nib mounted to an elongate inkcartridge such that the cartridge extends along the longitudinal axis ofthe nib, proximate the apex of the substantially triangular crosssection.

Optionally, the stylus further comprises an elongate battery mountedalong the base of the triangular cross section, opposite the apex.

Optionally, the stylus further comprises a printed circuit board mountedbetween the battery and the cartridge.

Optionally, the sensor has an image sensor and lens for capturing imagesof the coded data when the sensor is in an operative position relativeto the surface;

-   -   the sensor further comprising a plurality of light sources for        illuminating the coded data for the image sensor, the light        sources each configured for illuminating an area of the surface        such that there is a common region illuminated by all the light        sources; wherein during use,    -   at least one of the light sources is selectively extinguishable        while at least one of the light sources provides sufficient        illumination for image capture.

Optionally, the plurality if light sources are two LEDs mounted oneither side of the lens.

Optionally, the substantially triangular cross section extends thelength of the elongate casing.

Optionally, the substantially triangular cross section has roundedcorners.

Optionally, the substantially triangular cross section approximates anequilateral triangle.

Hand-Held Optical Sensor with Multiple Light Sources

Background

The Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface). A source of light in the opticalsensor brightly illuminates the surface so that an image of the codeddata on the paper is focused by a lens onto the active region of animage sensor. The spectral emission peak of the light source is matchedto the spectral absorption peak of the ink used to print the coded datato maximise contrast in captured image.

Unfortunately, as the pen is hand-held, it may be held to the paper atan angle that causes reflections from the light source that aredetrimental to the image sensor. Glossy paper is particularly prone tothis and the user is not likely to realise that any failure of theoptical sensor to read the coded data is caused by the angle at whichthey are holding the pen.

Summary

Accordingly, this aspect provides a hand-held optical sensor for sensingcoded data disposed on a surface, the sensor comprising:

-   -   an image sensor and lens for capturing images of the coded data        when the optical sensor is in an operative position relative to        the surface;    -   a plurality of light sources for illuminating the coded data for        the image sensor, the light sources each configured for        illuminating an area of the surface such that there is a common        region illuminated by all the light sources; wherein during use,    -   at least one of the light sources is selectively extinguishable        while at least one of the light sources provides sufficient        illumination for image capture.

The use of two light sources that can be individually selected allowsdynamic avoidance of undesirable reflections when the pen is held atsome angles, especially on glossy paper. It also ensures a more uniformillumination of the coded data.

Optionally, the plurality of light sources are two illumination sourcesmounted on opposite sides of the lens.

Optionally, the two illumination sources have intersecting axes ofillumination. Optionally, the optical sensor further comprises a controlunit connected to the image sensor and the two illumination sources suchthat the control unit extinguishes one of the two illumination sourcesupon detection of undesirable reflection from the surface. Optionallythe control unit predicts undesirable reflection from the surface usingpast detection of the undesirable reflection. Optionally, the controlunit uses one or more captured images to compute the position of thestylus relative to the surface in order to predict when undesirablereflection will occur.

End Cap Switch for Electronic Stylus

Background

The Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface).

For convenience the electronics within the pen are powered by arechargeable battery. This affords the pen a high degree of portabilityis likely to be carried about by the user for much of the day. Howeverthere will be prolonged periods where the pen is not used and it isinconvenient to return it to a battery recharger. To preserve thebattery the user should ideally switch the pen off after each use.Unfortunately, users often forget to turn off the pen after each andevery use. The pen can automatically power down after a set period ofbeing idle. However a significant amount of battery power is wastedduring the idle period.

Summary

Accordingly, this aspect provides an electronic stylus and end capassembly comprising:

-   -   a stylus with an elongate casing that houses battery powered        electronic components;    -   electrical contacts exposed by an opening in the elongate        casing; and,    -   a cap that fits over one end of the stylus, the cap having a        conductive portion positioned such that fitting the cap over        said one end of the stylus electrically connects the contacts to        control power to the electronic components.

By linking the power switch to the removal and replacement of the endcap, the pen is only active when it is uncapped. Whenever it is capped(and therefore not in use) it switched to a low power state to conservepower and extend battery life. The contacts of the on/off switch can beproximate the nib, in which case fitting the cap over the nib andclosing the switch deactivates the pen. Alternatively the contacts canbe at the opposite end of the pen and the cap closes the contacts toactivate the pen immediately before use.

Optionally, the electronic stylus further comprises a nib at said oneend of the elongate casing and fitting the cap over the nib, and theelectrical contacts are proximate the nib such that fitting the cap overthe nib switches the stylus to a low power inactive state.

Optionally, the stylus is configured to use the electrical contacts torecharge the battery.

Optionally, the conductive portion in the cap is a conductiveelastomeric molding.

Optionally, the nib is a ball point nib and the stylus further comprisesan tubular ink cartridge and a structure defining a cavity for retainingthe ink cartridge, the structure having an open end for axiallyreceiving the ink cartridge as it is slid into the cavity; wherein,

-   -   the open end of the structure is at least partially formed by        the electrical contacts.

Optionally, the structure has conductive sections connected to theelectrical contacts for transmitting power to the battery. Optionally,the structure is tubular with an internal conductive layer insulatedfrom an outer conductive layer by an insulating layer.

Ink Cartridge with Inbuilt Cartridge Removal Tool

Background

The Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface).

One of the primary features of the Netpage pen is its ability to ‘click’on interactive elements on a Netpage in the same way a mouse can clickon screen-based interactive elements (e.g. hyperlinks and so on).However, with a Netpage pen, the user simply puts the nib on theinteractive element in order to click on it. The optical sensoridentifies the element via its unique page and page location while aforce sensor registers a ‘pen down’ condition when the nib is pressedagainst the page. Registering ‘pen down’ and ‘pen up’ is alsofundamental to capturing the users handwriting on Netpage input fields.

For optimal operation, the cartridge should be securely coupled to theforce sensor. However, the cartridge should be easily de-coupled fromthe force sensor whenever it is replaced with a fresh cartridge.

Summary

Accordingly this aspect provides an ink cartridge for insertion into astylus, the ink cartridge comprising:

-   -   an elongate body for containing a supply of ink, the elongate        body having a nib end and an opposing end; and    -   an engagement formation at the opposing end for engaging the nib        end of another ink cartridge of the same type in the stylus in        order to extract it from the stylus.

By forming the customized removal tool on the cartridge itself, it willalways be convenient to the user when a spent cartridge is to bereplaced. The tool allows the user to grip the replacement cartridge forbetter purchase and more force when removing the existing cartridge fromthe stylus. With a greater extracting force, the releasable couplingbetween the cartridge and the force sensor can be tighter and moresecure. Furthermore, extracting the cartridge through the nib end of thepen rather than the back (as is the case with many conventional pens)minimizes pen disassembly and the force sensor can remain in place.

Optionally, the nib end has a writing nib in fluid communication withthe supply of ink.

Electronic Stylus with Recharging Contacts at Ink Cartridge ReceptacleOpening

Background

The Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is usually an electronic stylus with a writing niband an optical sensor for reading a pattern of coded data on the paper(or other surface).

For convenience the electronics within the pen are powered by arechargeable battery. Typically the pen is used frequently throughoutthe day with many intervening periods when the pen is not used. Thebattery can be sized to accommodate a full day's use before overnightrecharging. However, it will be appreciated that battery size directlyaffects the overall size and weight of the pen. To keep the battery sizedown to a practical size, the user should be encouraged to connect thepen to the recharger when it is not in use. In light of this, connectingthe pen to the recharger should be quick and simple for the user.

Summary

Accordingly this aspect provides an electronic stylus comprising:

-   -   an outer casing housing electronic components and a rechargeable        battery;    -   a structure defining a receptacle for retaining an ink cartridge        with a ball point nib at one end, the structure having an open        end for axially receiving the ink cartridge as it is slid into        the receptacle; wherein,    -   the open end of the structure is at least partially formed by        electrical contacts configured for connection to complementary        contacts within a battery recharger.

Putting the recharging contacts at the opening of the ink cartridgereceptacle allows the pen to be simply placed into a cup style rechargerwhen the pen is not being used. The internal shape of the recharger canbe formed so that the outer casing and/or the nib accurately guides therecharging contacts into engagement with the complementary contacts. Inthis way, the recharger can effectively double as a pen holder on theuser's desk.

Optionally, the structure has conductive sections connected to theelectrical contacts for transmitting power to the battery. Optionally,the structure is tubular with an internal conductive layer insulatedfrom an outer conductive layer by an insulating layer.

Optionally, the stylus further comprises a cap that fits over the nib,the cap having a conductive portion positioned such that fitting the capover the nib switches the stylus to a low power inactive state.

Optionally, the stylus further comprises a printed circuit board (PCB)wherein the internal conductive layer and the outer conductive layerengage respective electrical contacts on the PCB.

Pre-Loaded Force Sensor

Background

The Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface).

One of the primary features of the Netpage pen is its ability to ‘click’on interactive elements on a Netpage in the same way a mouse can clickon screen-based interactive elements (e.g. hyperlinks and so on).However, with a Netpage pen, the user simply puts the nib on theinteractive element in order to click on it. The optical sensoridentifies the element via its unique page and location ID while a forcesensor registers a ‘pen down’ condition when the nib is pressed againstthe page. Registering ‘pen down’ and ‘pen up’ is also fundamental tocapturing the user's handwriting on Netpage input fields. Non-binaryforce signals are also captured for reproducing hand-drawn strokes withvarying force-related width and opacity. Force variation can also beused as one of the dimensions examined during signature verification.

To accurately sense relatively light forces (such as the force ofhandwriting on a nib) the force sensor needs to be mounted against thenib or cartridge with very fine tolerances. With a full span movement ofsensor being relatively small (typically less than 50 microns),positioning the force sensor and the replaceable cartridge withsufficiently accuracy can be prohibitively difficult and commerciallyimpractical for a mass produced article.

Summary

Accordingly, this aspect provides a force sensor comprising:

-   -   a load bearing structure for contact with an input member        subject to a force to be sensed;    -   a sensor circuit for converting a force applied to the load        bearing structure into a signal indicative of the force; and,    -   a pre-load bias assembly for engaging the input member to bias        it against the load bearing structure.

By keeping the input member biased against the load bearing structure ofthe sensor, accurately mounting the sensor next to the input member isno longer an issue. The biasing mechanism can be a simple springstructure while still providing a suitably consistent biasing force.Such a mechanism has relatively low production costs and avoids the needto adhere to fine tolerances.

Optionally, the pre-load bias assembly has a spring and engagementformations for releasably engaging the input member. Optionally, thesensor circuit is a piezoresistive bridge circuit. Optionally the sensorcircuit is a capacitative or inductive force sensing circuit.Optionally, the sensor circuit senses forces up to about 500 grams (5Newtons). Optionally the signal output from the sensor circuit supportsa hand writing recognition facility. Optionally the load bearingstructure has a 10 micron full span movement during operation.Optionally, the pre-load bias assembly applies a bias of about 10 gramsto 20 grams (0.1 Newtons to 0.2 Newtons).

Optionally, the input member is an ink cartridge within a writingstylus. Optionally the load bearing structure has an elastomeric memberto absorb shock loads to the input member.

In a closely related aspect, there is provided an electronic styluscomprising:

-   -   an elongate molding;    -   a nib at one end of the elongate molding; and,    -   a force sensor mounted to the elongate molding, the force sensor        having a load bearing structure for contact with an input member        connected to the nib, a sensor circuit for converting a force        applied to the nib into a signal indicative of the force, and a        pre-load bias assembly for engaging the input member to bias it        against the load bearing structure.

Optionally, the nib is a ball point nib and the input member is an inkcartridge in fluid communication with the nib.

Pen with Side Loading Cartridge

Background

This Netpage system involves the interaction between a user and acomputer network (or stand alone computer) via a pen and paper basedinterface. The ‘pen’ is an electronic stylus with a marking ornon-marking nib and an optical sensor for reading a pattern of codeddata on the paper (or other surface).

The Netpage pen is an electronic stylus with force sensing, opticalsensing and Bluetooth communication assemblies. A significant number ofelectronic components need to be housed within the pen casing togetherwith a battery large enough to provide a useful battery life. Despitethis, the overall dimensions of the pen need to be small enough for auser to manipulate it as they would a normal pen.

If the Netpage pen has a ballpoint nib, the ink cartridge must be keptas small as possible to conserve space within the pen casing, yet not sosmall that it needs to be replaced too frequently. Furthermore, theforce sensor is best located at the end of the cartridge axiallyopposite the nib. This effectively precludes retracting the cartridgethrough the top (non-writing end) of the pen without disassembling muchof the pen.

Beyond the Netpage context, most ink pens have cartridges that need tobe inserted or withdrawn through the ends of the tubular pen casing.This imposes structural restrictions of the shape of the cartridge andtherefore its ink storage capacity.

Summary

Accordingly, this aspect provides a pen comprising:

-   -   an elongate chassis molding; and,    -   a cartridge with a nib and an elongate body; wherein,    -   the cartridge is configured for insertion and removal from the        elongate chassis mold from a direction transverse to the        longitudinal axis of the chassis molding.

Optionally, the cartridge is an ink cartridge and the elongate bodyhouses an ink reservoir.

According to a closely related aspect, the present invention provides anink cartridge for a pen, the ink cartridge comprising:

-   -   an elongate ink reservoir; and,    -   a writing nib in fluid communication with the ink reservoir;        wherein,    -   the elongate ink reservoir has an enlarged transverse cross        section along a portion of its length intermediate its ends.

By configuring the pen chassis and cartridge so that it can be insertedand removed from the side rather than through the ends, the capacity ofthe cartridge can be significantly increased. An enlarged sectionbetween the ends of the ink cartridge increases the capacity whileallowing the relatively thin ends to be supported at the nib molding andopposing end of the pen chassis. In a Netpage pen, inserting thecartridge from the side avoids the need to remove the force sensor whenreplacing the cartridge. Again, the thinner sections at each end of thecartridge allow it to engage a ball point nib supported in the nibmolding and directly engage the force sensor at the other end, while theenlarged middle portion increases the ink capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings in which:

FIG. 1 shows the structure of a complete tag;

FIG. 2 shows a symbol unit cell;

FIG. 3 shows nine symbol unit cells;

FIG. 4 shows the bit ordering in a symbol;

FIG. 5 shows a tag with all bits set;

FIG. 6 shows a tag group made up of four tag types;

FIG. 7 shows the continuous tiling of tag groups;

FIG. 8 shows the interleaving of codewords A, B, C & D within a tag;

FIG. 9 shows a codeword layout;

FIG. 10 shows a tag and its eight immediate neighbours labelled with itscorresponding bit index;

FIG. 11 shows a nib and elevation of the pen held by a user;

FIG. 12 shows the pen held by a user at a typical incline to a writingsurface;

FIG. 13 is a lateral cross section through the pen;

FIG. 14A is a bottom and nib end partial perspective of the pen;

FIG. 14B is a bottom and nib end partial perspective with the fields ofillumination and field of view of the sensor window shown in dottedoutline;

FIG. 15 is a partial perspective of the USB cable and USB socket in thetop end of the pen;

FIG. 16 is an exploded perspective of the pen components;

FIG. 17 is a longitudinal cross section of the pen;

FIG. 18 is a partial longitudinal cross section of the cap placed overthe nib end of the pen;

FIG. 19 is an exploded perspective of the optics assembly;

FIG. 20 is an exploded perspective of the force sensor assembly;

FIG. 21 is an exploded perspective of the ink cartridge tube and nibengaging removal tool;

FIG. 22 is a partially sectioned perspective of a new ink cartridgeengaging the nib end of the currently installed ink cartridge;

FIG. 23 is a partial perspective of the packaged force sensor on themain PCB;

FIG. 24 is a longitudinal cross section of the force sensor and main PCBshown in FIG. 15;

FIG. 25 is an exploded perspective of the cap assembly;

FIG. 26 is a circuit diagram of the pen USB and power CCT's;

FIG. 27A is a partial longitudinal cross section of the nib and barrelmolding;

FIG. 27B is a partial longitudinal cross section of the IR LED's and thebarrel molding;

FIG. 28 is a ray trace of the pen optics adjacent a sketch of the inkcartridge;

FIG. 29 is a side elevation of the lens;

FIG. 30 is a side elevation of the nib and the field of view of theoptical sensor;

FIG. 31 is an exploded perspective of the pad;

FIG. 32 is a longitudinal cross section of the pad with the peninserted;

FIG. 33 is a schematic representation of the force sensor assembly;

FIG. 34 is a schematic representation of a top-loading ink cartridge andforce sensor;

FIG. 35 is a schematic representation of a top loading ink cartridgeinto a pen with a retaining cavity for the pre-load spring;

FIG. 36 is a block diagram of the pen electronics;

FIG. 37 show the charging and connection options for the pen and thepod;

FIGS. 38A to 38E show the various components of the packaged forcesensor;

FIG. 39 is a bottom perspective of the main PCB with the Bluetoothantenna shield removed;

FIG. 40 is a top perspective of the main PCB;

FIG. 41 is a bottom perspective of the chassis molding and elastomericand cap;

FIG. 42A is a perspective of the optics assembly lifted from the chassismolding;

FIG. 42B is an enlarged partial perspective of the optics assemblyseated in the chassis molding;

FIG. 43A is a bottom perspective of the force sensor assembly partiallyinstalled in the chassis molding;

FIG. 43B is a bottom perspective of the force sensing assembly installedin the chassis molding;

FIG. 44 is a bottom perspective of the battery and main PCB partiallyinstalled in the chassis molding;

FIG. 45 is a bottom perspective of the chassis molding with the basemolding lifted clear;

FIGS. 46A and 46B are enlarged partial perspectives showing the coldstake on the chassis molding being swaged and sealed to the basemolding;

FIG. 47 is a bottom perspective of the product label being fixed to thebase molding;

FIG. 48 is an enlarged partial perspective of the nib molding beinginserted on the chassis molding;

FIG. 49 is a perspective of the tube molding being inserted over thechassis molding;

FIG. 50 is a perspective of the cap assembly being placed on the nibmolding;

FIG. 51 is a diagram of the major power states of the pen; and,

FIG. 52 is a diagram of the operational states of the Bluetooth module.

DETAILED DESCRIPTION

As discussed above, the invention is well suited for incorporation inthe Assignee's Netpage system. In light of this, the invention has beendescribed as a component of a broader Netpage architecture. However, itwill be readily appreciated that electronic styli have much broaderapplication in many different fields. Accordingly, the present inventionis not restricted to a Netpage context.

Netpage Surface Coding

Introduction

This section defines a surface coding used by the Netpage system(described in co-pending application Docket No. NPS110US as well as manyof the other cross referenced documents listed above) to imbue otherwisepassive surfaces with interactivity in conjunction with Netpage sensingdevices (described below).

When interacting with a Netpage coded surface, a Netpage sensing devicegenerates a digital ink stream which indicates both the identity of thesurface region relative to which the sensing device is moving, and theabsolute path of the sensing device within the region.

Surface Coding

The Netpage surface coding consists of a dense planar tiling of tags.Each tag encodes its own location in the plane. Each tag also encodes,in conjunction with adjacent tags, an identifier of the regioncontaining the tag. In the Netpage system, the region typicallycorresponds to the entire extent of the tagged surface, such as one sideof a sheet of paper.

Each tag is represented by a pattern which contains two kinds ofelements. The first kind of element is a target. Targets allow a tag tobe located in an image of a coded surface, and allow the perspectivedistortion of the tag to be inferred. The second kind of element is amacrodot. Each macrodot encodes the value of a bit by its presence orabsence.

The pattern is represented on the coded surface in such a way as toallow it to be acquired by an optical imaging system, and in particularby an optical system with a narrowband response in the near-infrared.The pattern is typically printed onto the surface using a narrowbandnear-infrared ink.

Tag Structure

FIG. 1 shows the structure of a complete tag 200. Each of the four blackcircles 202 is a target. The tag 200, and the overall pattern, hasfour-fold rotational symmetry at the physical level.

Each square region represents a symbol 204, and each symbol representsfour bits of information. Each symbol 204 shown in the tag structure hasa unique label 216. Each label 216 has an alphabetic prefix and anumeric suffix. FIG. 2 shows the structure of a symbol 204. It containsfour macrodots 206, each of which represents the value of one bit by itspresence (one) or absence (zero).

The macrodot 206 spacing is specified by the parameter s throughout thisspecification. It has a nominal value of 143 μm, based on 9 dots printedat a pitch of 1600 dots per inch. However, it is allowed to vary withindefined bounds according to the capabilities of the device used toproduce the pattern.

FIG. 3 shows an array 208 of nine adjacent symbols 204. The macrodot 206spacing is uniform both within and between symbols 208.

FIG. 4 shows the ordering of the bits within a symbol 204.

Bit zero 210 is the least significant within a symbol 204; bit three 212is the most significant. Note that this ordering is relative to theorientation of the symbol 204. The orientation of a particular symbol204 within the tag 200 is indicated by the orientation of the label 216of the symbol in the tag diagrams (see for example FIG. 1). In general,the orientation of all symbols 204 within a particular segment of thetag 200 is the same, consistent with the bottom of the symbol beingclosest to the centre of the tag.

Only the macrodots 206 are part of the representation of a symbol 204 inthe pattern. The square outline 214 of a symbol 204 is used in thisspecification to more clearly elucidate the structure of a tag 204. FIG.5, by way of illustration, shows the actual pattern of a tag 200 withevery bit 206 set. Note that, in practice, every bit 206 of a tag 200can never be set.

A macrodot 206 is nominally circular with a nominal diameter of (5/9)s.However, it is allowed to vary in size by ±10% according to thecapabilities of the device used to produce the pattern.

A target 202 is nominally circular with a nominal diameter of (17/9)s.However, it is allowed to vary in size by ±10% according to thecapabilities of the device used to produce the pattern.

The tag pattern is allowed to vary in scale by up to ±10% according tothe capabilities of the device used to produce the pattern. Anydeviation from the nominal scale is recorded in the tag data to allowaccurate generation of position samples.

Tag Groups

Tags 200 are arranged into tag groups 218. Each tag group contains fourtags arranged in a square. Each tag 200 has one of four possible tagtypes, each of which is labelled according to its location within thetag group 218. The tag type labels 220 are 00, 10, 01 and 11, as shownin FIG. 6.

FIG. 7 shows how tag groups are repeated in a continuous tiling of tags,or tag pattern 222. The tiling guarantees the any set of four adjacenttags 200 contains one tag of each type 220.

Codewords

The tag contains four complete codewords. The layout of the fourcodewords is shown in FIG. 8. Each codeword is of a punctured 2⁴-ary (8,5) Reed-Solomon code. The codewords are labelled A, B, C and D.Fragments of each codeword are distributed throughout the tag 200.

Two of the codewords are unique to the tag 200. These are referred to aslocal codewords 224 and are labelled A and B. The tag 200 thereforeencodes up to 40 bits of information unique to the tag.

The remaining two codewords are unique to a tag type, but common to alltags of the same type within a contiguous tiling of tags 222. These arereferred to as global codewords 226 and are labelled C and D,subscripted by tag type. A tag group 218 therefore encodes up to 160bits of information common to all tag groups within a contiguous tilingof tags.

Reed-Solomon Encoding

Codewords are encoded using a punctured 2⁴-ary (8, 5) Reed-Solomon code.A 2⁴-ary (8, 5) Reed-Solomon code encodes 20 data bits (i.e. five 4-bitsymbols) and 12 redundancy bits (i.e. three 4-bit symbols) in eachcodeword. Its error-detecting capacity is three symbols. Itserror-correcting capacity is one symbol.

FIG. 9 shows a codeword 228 of eight symbols 204, with five symbolsencoding data coordinates 230 and three symbols encoding redundancycoordinates 232. The codeword coordinates are indexed in coefficientorder, and the data bit ordering follows the codeword bit ordering.

A punctured 2⁴-ary (8, 5) Reed-Solomon code is a 2⁴-ary (15, 5)Reed-Solomon code with seven redundancy coordinates removed. The removedcoordinates are the most significant redundancy coordinates.

The code has the following primitive polynominal:p(x)=x ⁴ +x+1  (EQ 1)

The code has the following generator polynominal:g(x)=(x+α)(x+α ²) . . . (x+α ¹⁰)  (EQ 2)

For a detailed description of Reed-Solomon codes, refer to Wicker, S. B.and V. K. Bhargava, eds., Reed-Solomon Codes and Their Applications,IEEE Press, 1994, the contents of which are incorporated herein byreference.

The Tag Coordinate Space

The tag coordinate space has two orthogonal axes labelled x and yrespectively. When the positive x axis points to the right, then thepositive y axis points down.

The surface coding does not specify the location of the tag coordinatespace origin on a particular tagged surface, nor the orientation of thetag coordinate space with respect to the surface. This information isapplication-specific. For example, if the tagged surface is a sheet ofpaper, then the application which prints the tags onto the paper mayrecord the actual offset and orientation, and these can be used tonormalise any digital ink subsequently captured in conjunction with thesurface.

The position encoded in a tag is defined in units of tags. Byconvention, the position is taken to be the position of the centre ofthe target closest to the origin.

Tag Information Content

Table 1 defines the information fields embedded in the surface coding.Table 2 defines how these fields map to codewords. TABLE 1 Fielddefinitions field width description per codeword codeword type 2 Thetype of the codeword, i.e. one of A (b′00′), B (b′01′), C (b′10′) and D(b′11′). per tag tag type 2 The type¹ of the tag, i.e. one of 00(b′00′), 01 (b′01′), 10 (b′10′) and 11 (b′11′). x coordinate 13 Theunsigned x coordinate of the tag². y coordinate 13 The unsigned ycoordinate of the tag^(b). active area flag 1 A flag indicating whetherthe tag is a member of an active area. b′1′ indicates membership. activearea map 1 A flag indicating whether an active area map flag is present.b′1′ indicates the presence of a map (see next field). If the map isabsent then the value of each map entry is derived from the active areaflag (see previous field). active area map 8 A map³ of which of thetag's immediate eight neighbours are members of an active area. b′1′indicates membership. data fragment 8 A fragment of an embedded datastream. Only present if the active area map is absent. per tag groupencoding format 8 The format of the encoding. 0: the present encodingOther values are TBA. region flags 8 Flags controlling theinterpretation and routing of region-related information. 0: region IDis an EPC 1: region is linked 2: region is interactive 3: region issigned 4: region includes data 5: region relates to mobile applicationOther bits are reserved and must be zero. tag size 16 The differencebetween the actual tag size adjustment and the nominal tag size⁴, in 10nm units, in sign-magnitude format. region ID 96 The ID of the regioncontaining the tags. CRC 16 A CRC⁵ of tag group data. total 320¹corresponds to the bottom two bits of the x and y coordinates of thetag²allows a maximum coordinate value of approximately 14 m³ FIG. 29 indicates the bit ordering of the map⁴the nominal tag size is 1.7145 mm (based on 1600 dpi, 9 dots permacrodot, and 12 macrodots per tag)⁵CCITT CRC-16 [7]

FIG. 10 shows a tag 200 and its eight immediate neighbours, eachlabelled with its corresponding bit index in the active area map. Anactive area map indicates whether the corresponding tags are members ofan active area. An active area is an area within which any capturedinput should be immediately forwarded to the corresponding Netscapeserver for interpretation. It also allows the Netpage sensing device tosignal to the user that the input will have an immediate effect. TABLE 2Mapping of fields to codewords codeword field codeword bits field widthbits A 1:0 codeword type 2 all (b′00′) 10:2  x coordinate 9 12:4  19:11y coordinate 9 12:4  B 1:0 codeword type 2 all (b′01′)  2 tag type 1 05:2 x coordinate 4 3:0  6 tag type 1 1 9:6 y coordinate 4 3:0 10 activearea flag 1 all 11 active area map flag 1 all 19:12 active area map 8all 19:12 data fragment 8 all C₀₀ 1:0 codeword type 2 all (b′10′) 9:2encoding format 8 all 17:10 region flags 8 all 19:18 tag size adjustment2 1:0 C₀₁ 1:0 codeword type 2 all (b′10′) 15:2  tag size adjustment 1415:2  19:16 region ID 4 3:0 C₁₀ 1:0 codeword type 2 all (b′10′) 19:2 region ID 18 21:4  C₁₁ 1:0 codeword type 2 all (b′10′) 19:2  region ID18 39:22 D₀₀ 1:0 codeword type 2 all (b′11′) 19:2  region ID 18 57:40D₀₁ 1:0 codeword type 2 all (b′11′) 19:2  region ID 18 75:58 D₁₀ 1:0codeword type 2 all (b′11′) 19:2  region ID 18 93:76 D₁₁ 1:0 codewordtype 2 all (b′11′) 3:2 region ID 2 95:94 19:4  CRC 16 all

Note that the tag type can be moved into a global codeword to maximiselocal codeword utilization. This in turn can allow larger coordinatesand/or 16-bit data fragments (potentially configurably in conjunctionwith coordinate precision). However, this reduces the independence ofposition decoding from region ID decoding and has not been included inthe specification at this time.

Embedded Data

If the “region includes data” flag in the region flags is set then thesurface coding contains embedded data. The data is encoded in multiplecontiguous tags' data fragments, and is replicated in the surface codingas many times as it will fit.

The embedded data is encoded in such a way that a random and partialscan of the surface coding containing the embedded data can besufficient to retrieve the entire data. The scanning system reassemblesthe data from retrieved fragments, and reports to the user whensufficient fragments have been retrieved without error.

As shown in Table 3, a 200-bit data block encodes 160 bits of data. Theblock data is encoded in the data fragments of A contiguous group of 25tags arranged in a 5×5 square. A tag belongs to a block whose integercoordinate is the tag's coordinate divided by 5. Within each block thedata is arranged into tags with increasing x coordinate withinincreasing y coordinate.

A data fragment may be missing from a block where an active area map ispresent. However, the missing data fragment is likely to be recoverablefrom another copy of the block.

Data of arbitrary size is encoded into a superblock consisting of acontiguous set of blocks arranged in a rectangle. The size of thesuperblock is encoded in each block. A block belongs to a superblockwhose integer coordinate is the block's coordinate divided by thesuperblock size. Within each superblock the data is arranged into blockswith increasing x coordinate within increasing y coordinate.

The superblock is replicated in the surface coding as many times as itwill fit, including partially along the edges of the surface coding.

The data encoded in the superblock may include more precise typeinformation, more precise size information, and more extensive errordetection and/or correction data. TABLE 3 Embedded data block fieldwidth description data type 8 The type of the data in the superblock.Values include: 0: type is controlled by region flags 1: MIME Othervalues are TBA. superblock width 8 The width of the superblock, inblocks. superblock height 8 The height of the superblock, in blocks.data 160 The block data. CRC 16 A CRC⁶ of the block data. total 200⁶CCITT CRC-16 [7]Cryptographic Signature of Region ID

If the “region is signed” flag in the region flags is set then thesurface coding contains a 160-bit cryptographic signature of the regionID. The signature is encoded in a one-block superblock.

In an online environment any signature fragment can be used, inconjunction with the region ID, to validate the signature. In an offlineenvironment the entire signature can be recovered by reading multipletags, and can then be validated using the corresponding public signaturekey. This is discussed in more detail in Netpage Surface Coding Securitysection of the cross reference co-pending application Docket No.NPS100US, which is entirely incorporated into the application withdocket no. NPS101US.

MIME Data

If the embedded data type is “MIME” then the superblock containsMultipurpose Internet Mail Extensions (MIME) data according to RFC 2045(see Freed, N., and N. Borenstein, “Multipurpose Internet MailExtensions (MIME)—Part One: Format of Internet Message Bodies”, RFC2045, November 1996), RFC 2046 (see Freed, N., and N. Borenstein,“Multipurpose Internet Mail Extensions (MIME)—Part Two: Media Types”,RFC 2046, November 1996) and related RFCs. The MIME data consists of aheader followed by a body. The header is encoded as a variable-lengthtext string preceded by an 8-bit string length. The body is encoded as avariable-length type-specific octet stream preceded by a 16-bit size inbig-endian format.

The basic top-level media types described in RFC 2046 include text,image, audio, video and application. RFC 2425 (see Howes, T., M. Smithand F. Dawson, “A MIME Content-Type for Directory Information”, RFC2045, September 1998) and RFC 2426 (see Dawson, F., and T. Howes, “vCardMIME Directory Profile”, RFC 2046, September 1998) describe a textsubtype for directory information suitable, for example, for encodingcontact information which might appear on a business card.

Encoding and Printing Considerations

The Print Engine Controller (PEC) supports the encoding of two fixed(per-page) 2⁴-ary (15, 5) Reed-Solomon codewords and six variable(per-tag) 2⁴-ary (15, 5) Reed-Solomon codewords. Furthermore, PECsupports the rendering of tags via a rectangular unit cell whose layoutis constant (per page) but whose variable codeword data may vary fromone unit cell to the next. PEC does not allow unit cells to overlap inthe direction of page movement. A unit cell compatible with PEC containsa single tag group consisting of four tags. The tag group contains asingle A codeword unique to the tag group but replicated four timeswithin the tag group, and four unique B codewords. These can be encodedusing five of PEC's six supported variable codewords. The tag group alsocontains eight fixed C and D codewords. One of these can be encodedusing the remaining one of PEC's variable codewords, two more can beencoded using PEC's two fixed codewords, and the remaining five can beencoded and pre-rendered into the Tag Format Structure (TFS) supplied toPEC.

PEC imposes a limit of 32 unique bit addresses per TFS row. The contentsof the unit cell respect this limit. PEC also imposes a limit of 384 onthe width of the TFS. The contents of the unit cell respect this limit.

Note that for a reasonable page size, the number of variable coordinatebits in the A codeword is modest, making encoding via a lookup tabletractable. Encoding of the B codeword via a lookup table may also bepossible. Note that since a Reed-Solomon code is systematic, only theredundancy data needs to appear in the lookup table.

Imaging and Decoding Considerations

The minimum imaging field of view required to guarantee acquisition ofan entire tag has a diameter of 39.6s (i.e. (2×(12+2))√{square root over(2)}s), allowing for arbitrary alignment between the surface coding andthe field of view. Given a macrodot spacing of 143 μm, this gives arequired field of view of 5.7 mm.

Table 4 gives pitch ranges achievable for the present surface coding fordifferent sampling rates, assuming an image sensor size of 128 pixels.TABLE 4 Pitch ranges achievable for present surface coding for differentsampling rates; dot pitch = 1600 dpi, macrodot pitch = 9 dots, viewingdistance = 30 mm, nib-to-FOV separation = 1 mm, image sensor size = 128pixels sampling rate pitch range 2 −40 to +49 2.5 −27 to +36 3 −10 to+18

Given the present surface coding, the corresponding decoding sequence isas follows:

-   -   locate targets of complete tag infer perspective transform from        targets    -   sample and decode any one of tag's four codewords    -   determine codeword type and hence tag orientation    -   sample and decode required local (A and B) codewords    -   codeword redundancy is only 12 bits, so only detect errors    -   on decode error flag bad position sample    -   determine tag x-y location, with reference to tag orientation    -   infer 3D tag transform from oriented targets    -   determine nib x-y location from tag x-y location and 3D        transform    -   determine active area status of nib location with reference to        active area map    -   generate local feedback based on nib active area status    -   determine tag type from A codeword    -   sample and decode required global (C and D) codewords (modulo        window alignment, with reference to tag type)    -   although codeword redundancy is only 12 bits, correct errors;    -   subsequent CRC verification will detect erroneous error        correction    -   verify tag group data CRC    -   on decode error flag bad region ID sample    -   determine encoding type, and reject unknown encoding    -   determine region flags    -   determine region ID    -   encode region ID, nib x-y location, nib active area status in        digital ink    -   route digital ink based on region flags

Note that region ID decoding need not occur at the same rate as positiondecoding.

Note that decoding of a codeword can be avoided if the codeword is foundto be identical to an already-known good codeword.

Netpage Pen

Functional Overview

The Netpage pen is a motion-sensing writing instrument which works inconjunction with a tagged Netpage surface (see Netpage Surface Codingand Netpage Surface Coding Security sections above). The penincorporates a conventional ballpoint pen cartridge for marking thesurface, a motion sensor for simultaneously capturing the absolute pathof the pen on the surface, an identity sensor for simultaneouslyidentifying the surface, a force sensor for simultaneously measuring theforce exerted on the nib, and a real-time clock for simultaneouslymeasuring the passage of time.

While in contact with a tagged surface, as indicated by the forcesensor, the pen continuously images the surface region adjacent to thenib, and decodes the nearest tag in its field of view to determine boththe identity of the surface, its own instantaneous position on thesurface and the pose of the pen. The pen thus generates a stream oftimestamped position samples relative to a particular surface, andtransmits this stream to a Netpage server (see Netpage Architecturesection in co-pending application Docket No. NPS110US). The samplestream describes a series of strokes, and is conventionally referred toas digital ink (DInk). Each stroke is delimited by a pen down and a penup event, as detected by the force sensor.

The pen samples its position at a sufficiently high rate (nominally 100Hz) to allow a Netpage server to accurately reproduce hand-drawnstrokes, recognise handwritten text, and verify hand-written signatures.

The Netpage pen also supports hover mode in interactive applications. Inhover mode the pen is not in contact with the paper and may be somesmall distance above the surface of the paper (or tablet etc.). Thisallows the position of the pen, including its height and pose to bereported. In the case of an interactive application the hover modebehaviour can be used to move the cursor without marking the paper, orthe distance of the nib from the coded surface could be used for toolbehaviour control, for example an air brush function.

The pen includes a Bluetooth radio transceiver for transmitting digitalink via a relay device to a Netpage server. When operating offline froma Netpage server the pen buffers captured digital ink in non-volatilememory. When operating online to a Netpage server the pen transmitsdigital ink in real time.

The pen is supplied with a docking cradle or “pod”. The pod contains aBluetooth to USB relay. The pod is connected via a USB cable to acomputer which provides communications support for local applicationsand access to Netpage services.

The pen is powered by a rechargeable battery. The battery is notaccessible to or replaceable by the user. Power to charge the pen can betaken from the USB connection or from an external power adapter throughthe pod. The pen also has a power and USB-compatible data socket toallow it to be externally connected and powered while in use.

The pen cap serves the dual purpose of protecting the nib and theimaging optics when the cap is fitted and signalling the pen to leave apower-preserving state when uncapped.

Pen Form Factor

The overall weight (45 g), size and shape (159 mm×17 mm) of the Netpagepen fall within the conventional bounds of hand-held writinginstruments.

Ergonomics and Layout

FIG. 11 shows a rounded triangular profile gives the pen 400 anergonomically comfortable shape to grip and use the pen in the correctfunctional orientation. It is also a practical shape for accommodatingthe internal components. A normal pen-like grip naturally conforms to atriangular shape between thumb 402, index finger 404 and middle finger406.

As shown in FIG. 12, a typical user writes with the pen 400 at a nominalpitch of about 30 degrees from the normal toward the hand 408 when held(positive angle) but seldom operates a pen at more than about 10 degreesof negative pitch (away from the hand). The range of pitch angles overwhich the pen 400 is able to image the pattern on the paper has beenoptimised for this asymmetric usage. The shape of the pen 400 helps toorient the pen correctly in the user's hand 408 and to discourage theuser from using the pen “upside-down”. The pen functions “upside-down”but the allowable tilt angle range is reduced.

The cap 410 is designed to fit over the top end of the pen 400, allowingit to be securely stowed while the pen is in use. Multi colour LEDsilluminate a status window 412 in the top edge (as in the apex of therounded triangular cross section) of the pen 400 near its top end. Thestatus window 412 remains un-obscured when the cap is stowed. Avibration motor is also included in the pen as a haptic feedback system(described in detail below).

As shown in FIG. 13, the grip portion of the pen has a hollow chassismolding 416 enclosed by a base molding 528 to house the othercomponents. The ink cartridge 414 for the ball point nib (not shown)fits naturally into the apex 420 of the triangular cross section,placing it consistently with the user's grip. This in turn providesspace for the main PCB 422 in the centre of the pen and for the battery424 in the base of the pen. By referring to FIG. 14 a, it can be seenthat this also naturally places the tag-sensing optics 426 unobtrusivelybelow the nib 418 (with respect to nominal pitch). The nib molding 428of the pen 400 is swept back below the ink cartridge 414 to preventcontact between the nib molding 428 and the paper surface when the penis operated at maximum pitch.

As best shown in FIG. 14 b, the imaging field of view 430 emergesthrough a centrally positioned IR filter/window 432 below the nib 418,and two near-infrared illumination LEDs 434, 436 emerge from the twobottom corners of the nib molding 428. The use of two illumination LEDs434, 436 ensures a more uniform illumination field 438, 440.

As the pen is hand-held, it may be held at an angle that causesreflections from one of the LED's that are detrimental to the imagesensor. By providing more than one LED, the LED causing the offendingreflections can be extinguished.

Pen Feedback Indications

FIG. 17 is a longitudinal cross section through the centre-line if thepen 400 (with the cap 410 stowed on the end of the pen). The penincorporates red and green LEDs 444 to indicate several states, usingcolours and intensity modulation. A light pipe 448 on the LEDs 444transmit the signal to the status indicator window 412 in the tubemolding 416. These signal status information to the user includingpower-on, battery level, untransmitted digital ink, network connectionon-line, fault or error with an action.

A vibration motor 446 is used to haptically convey information to theuser for important verification functions during transactions. Thissystem is used for important interactive indications that might bemissed due to inattention to the LED indicators 444 or high levels ofambient light. The haptic system indicates to the user when:

-   -   The pen wakes from standby mode    -   There is an error with an action    -   To acknowledge a transaction        Pod Feedback Indications

Turning briefly to the recharging pod 450 shown in FIGS. 31 and 32, redand green LEDs 452 to indicate various states using colours andintensity modulation. The light from the LEDs is transmitted to theexterior of the pod via the polymer light pipe molding 454. These signalstatus information to the user including charging state, anduntransmitted digital ink by illuminating/pulsating one LEDs 452 at atime.

Features and Accessories

As shown in FIG. 15, the pen has a power and data socket 458 is locatedin the top end 456 of the pen, hidden and moisture-sealed behind anelastomeric end-cap 460. The end-cap can be prised open to give accessto the socket 458 and reset switch (at the bottom of recess 464) andremains open while the cable 462 is in use. The USB power and data cable462 allows the pen to be used for periods that exceed the battery life.

The usual method of charging the pen 400 is via the charging pod 450shown in FIGS. 31 and 32. As will be described in greater detail below,the pod 450 includes a Bluetooth transceiver connected by USB to acomputer and several LEDs to indicate for charging status. The pod iscompact to minimise its desktop footprint, and has a weighted base forstability. Data transfer occurs between the pen and the pod via aBluetooth radio link.

Market Differentiation

Digital mobile products and quality pens are usually considered aspersonal items. This pen product is used by both genders from 5 yearsupwards for personal, educational and business use, so many markets haveto be catered for. The pen design allows for substantial usercustomisation of the external appearance of the pen 400 and the pod 450by having user changeable parts, namely the cap 410, an outer tubemolding 466 (best shown in FIGS. 16 and 49) and the pod jacket 468 (bestshown in FIGS. 31 and 32). These parts are aquagraphic printed (a waterbased transfer system) to produce a variety of high quality graphicimages and textures over all surfaces of these parts. These parts areaccessories to the pen, allowing the user to change the appearancewhenever they wish. A number of licensed images provide enhancers forthe sale of accessories as an additional business model, similar to thepractice with mobile phone covers.

Pen Mechanical Design

Parts and Assemblies

Referring to FIG. 16, the pen 400 has been designed as a high volumeproduct and has four major sub-assemblies:

-   -   an optical assembly 470;    -   a force sensing assembly 474;    -   a cap assembly 472; and,    -   the main assembly 476, which holds the main PCB 422 and battery        424.

Wherever possible, moldings have been designed as line-of-draw to reducecost and promote longevity in the tooling.

These assemblies and the other major parts can be identified in FIG. 17.As the form factor of the pen is to be as small as possible these partsare packed as closely as practical. The electrical components in theupper part of the pen, namely the force sensor assembly 474 and thevibration motor 446 all have sprung contacts (512 of FIG. 24 and 480 ofFIG. 38A respectively) directly mating with contact pads 482 and 484respectively (see FIG. 40) on the PCB 422. This eliminates the need forconnectors and also decouples these parts from putting any stress ontothe main PCB.

Although certain individual molded parts are thin walled (0.8 to 1.2 mm)the combination of these moldings creates a strong structure. The pen isdesigned not to be user serviceable and therefore has a cold stake underthe exterior label to prevent user entry. Non-conducting plasticsmoldings are used wherever possible to allow an omnidirectional beampattern to be formed by the Bluetooth radio antenna 486 (see FIG. 40).

Optics Assembly

The major components of the optical assembly are as shown in FIGS. 18and 19. The axial alignment of the lens 488 to the image sensor 490 istoleranced to be better than 50 μm to minimise blur at the image. Thebarrel molding 492 is therefore has high precision with tighttolerancing. It has a molded-in aperture 494 near the image sensor 490,which provides the location for the lens 488. As the effect of thermalexpansion is very small on a molding this size, it is not necessary touse a more expensive material.

The flex PCB 496 mounts two infrared LEDs 434 and 436, a wire bondedChip-on-Flex image sensor 490 and some chip capacitors 502. The flex PCB496 is 75 micron thick polyimide, which allows the two infrared LEDs 434and 436 to be manipulated. Stiffeners are required in certain areas onthe flex as backing for the attached components. The flex PCB 496 islaser cut to provide accuracy for mounting onto the barrel molding 492and fine pitch connector alignment.

Force Sensing Assembly and Ink Cartridge

FIGS. 20, 23, 24 and 40 show the components and installation of theforce sensing assembly. The force sensing assembly 474 is designed toaccurately measure force put on the ink cartridge 414 during use. It isspecified to sense between 0 and 500 grams force with enough fidelity tosupport handwriting recognition in the Netpage services. This captiveassembly has two coaxial conductive metal tubes 498, a retainer spring504 and a packaged force sensor 500.

Conductive Metal Tube

The conductive metal tubes 498 has an insert molded insulation layer 506between two metal tubes (inner tube 508 and outer tube 510), which eachhave a sprung gold plated contact finger (512 and 514 respectively).Power for charging the battery is provided by two contacts 516 (see FIG.31) in the charging pod 450 and is conducted by these two tubes directlyto recharging contacts 518 and 520 (see FIG. 40) on the main PCB 422,via a spring contact (512 and 514 respectively) on each tube.

When the pen cap assembly 472 is placed on the front of the pen 400, aconductive elastomeric molding in the pen cap mates with the ends ofboth concentric tubes in the conductive metal tube part, completing thecircuit and signalling the cap presence to the pen electronics (see FIG.18).

Force Sensor Operating Principles

FIG. 33 schematically illustrates the operation of the force sensingassembly 474. The spring 700 applies a pre-load to the force sensor IC526 (via a ball bearing 524) before the cartridge 414 is subject to anyforce at the nib 418. The cartridge 414 itself is not pushed against theforce sensor as it passes through the spring. Instead, the spring pushesa boot 702 against the force sensor, and the boot is coupled to the endof the cartridge. The boot 702 is a compromise between allowing easymanual insertion and removal of cartridge 414, and ensuring thecartridge is held securely without travel. The use of a boot 702 alsoallows the inclusion of a stop surface 698. The stop limits the travelof the boot 702 thereby protecting the spring 700 from overload.

Packaged Force Sensor

FIGS. 38A to 38E are perspectives of the various components of thepackaged force sensor 500. FIG. 38A shows a steel ball 524 protrudingfrom the front of a sensor IC (chip) 526. The ball 524 is the pointcontact used to transmit force directly to the chip. Wire bonds 604connect the chip 526 to the spring contacts 478. The chip sits in therecess 564 formed in the rear molding 566 shown in FIG. 38B. A pressurerelief vent 584 in the base of the recess 564 allows air trapped by thechip 526 to escape. The front molding 606 shown in FIG. 38C, has slots608 in its underside for the sprung contacts 478 and a central aperture610 to hold the ball 524. Location details 612 mate with correspondingdetails in the coaxial conductive tubes 498 as shown in FIG. 24.

As there is only 10 microns full span movement in this system, themounting of this assembly in the pen and use of axial preload is tightlytoleranced. The force sensing assembly is mounted in the top of the penso that it can only stress the pen chassis molding 416 (see FIG. 16),and force will not be transmitted to the main PCB 422. The force sensoris a push fit onto the end of the inner conductive metal tube 508 alsotrapping the retainer spring 504, which makes a simple dedicatedassembly 500.

Retainer Spring

Turning to FIGS. 20 and 24, the retainer spring 504 is the equivalent tothe boot 702 described in FIG. 33. It is a high precision stamping outof thin sheet metal with an insulating layer 708 at the point where itcontacts the ball 524. This inhibits electrical interference with theforce sensor IC 526 caused by external electrostatic discharge via theink cartridge 414. The metal retainer spring 504 is formed into fourgripping arms 530 and two spring arms 532. A spent cartridge removaltool 534 is secured to the open end of the cartridge 414 with aninterference fit. The gripping arms 530 grip a complementary externalgrip profile 704 on the removal tool 534. The spring arms 532 extendbeyond the end of gripping arms 530 to press against the stepped section706 in the coaxial tube assembly 498. This in turn pushes insulated base708 against the ball 524 to put an accurate axial preload force ofbetween 10 and 20 grams onto the force sensor.

Ink Cartridge

The pen ink cartridge 414 is best shown in FIGS. 21A and 21B. Researchshows that industry practice is for the ballpoint nib 418 to be made byone source and the metal tube 536 to be made by another, along withassembly and filling. There are no front loading standard ink cartridgesthat meet the design capacity and form factor requirements so a customcartridge has been developed. This ink cartridge 414 has a 3 mm diametertube 536 with a standard ballpoint nib inserted. The spent cartridgeremoval tool 534 is a custom end molding that caps the open end of themetal tube 536.

The removal tool 536 contains an air vent 538 for ink flow, a locationdetail 540 and a co-molded elastomeric ring 542 around a recess 544detail used for extracting the spent ink cartridge. The tool is levereddown to engage the nib of the old cartridge and then drawn out throughthe nib end of the pen as shown in FIG. 21B. The elastomer ring 542reduces the possibility that a hard shock could damage the force sensorif the pen is dropped onto a hard surface.

The location detail 540 allows the ink cartridge 414 to accurately seatinto the retainer spring 504 in the force sensing assembly 474 and to bepreloaded against the force sensor 500. The removal tool (apart from theco-molded elastomeric ring) is made out of a hard plastic such as acetaland can be molded in color to match the ink contents. The ink capacityis 5 ml giving an expected write-out length comparable with standardballpoint ink cartridges. This capacity means that refill cycles will berelatively infrequent during the lifetime of the pen.

Force Sensing Method

Pressing the nib 418 against a surface will transfer the force to theball 524 via the gripping arms 530. The force from the nib adds to thepreload force from the spring arms 532. The force sensor is a push fitinto the end of the coaxial tube assembly 498 and both directly connectto the PCB with spring contacts (478 and 512 respecively). FIG. 24 showsthe limited space available for an axial force sensor, hence a packageddesign is required as off-the-shelf items have no chance of fitting inthis space envelope in the required configuration.

This force sensing arrangement detects the axial force applied to thecartridge 414, which is the simplest and most accurate solution. Thereis negligible friction in the system as the cartridge contacts only ontwo points, one at either end of the conductive metal barrel 498. Themetal retainer spring 504 will produce an accurate preload force up to20 grams onto the force sensor 500. This is seen to be a reliable systemover time, as the main parts are metal and therefore will not sufferfrom creep, wear or stiction during the lifetime of the pen.

This design also isolates the applied force by directing it onto thepackaged force sensor, which pushes against the solid seat in thechassis molding 416 of the pen. This allows the force sensing assembly474 to float above the main PCB 422 (so as not to put strain on it)whilst transmitting data via the spring contacts 478 at the base of thepackaged force sensor 500. The resulting assembly fits neatly into thepen chassis molding 416 and is easy to hand assemble.

Top/Side Loading Cartridge

As discussed above, the pen will require periodic replacement of the inkcartridge during its lifetime. While the front loading ink cartridgesystem is convenient for users, it can have some disadvantages. Frontloading limits the capacity of the ink reservoir in the cartridge, sincethe diameter of the cartridge along its full length is limited to theminimum cartridge diameter, as dictated by the constraints of the pennose.

The cartridge 414 must be pushed against the force sensor IC 526 (viathe steel ball 524) by a pre-load spring 700 (see FIG. 33). However, thecartridge 414 itself does not provide the face against which the springpushes, since the cartridge must pass through the spring. Thisnecessitates the boot 702 or retaining spring 504 discussed above.

The boot is necessarily a compromise between allowing easy manualinsertion and removal of cartridge, and ensuring the cartridge is heldsecurely without travel.

A ‘top-loading’ cartridge, as illustrated in FIG. 34, can overcome thesedisadvantages. It will be appreciated that ‘top loading’ is a referenceto insertion of the cartridge from a direction transverse to thelongitudinal axis of the pen. Because of the other components within thepen, it is most convenient to insert the cartridge from the ‘top’ orapex 420 of the pen's substantially triangular cross section (see FIG.13).

The pre-load spring 700 can be placed toward the nib 418 of thecartridge 414, thus providing a convenient mechanism for seating thecartridge against the force sensor ball 524 after insertion. A cartridgetravel stop 712 is formed on the chassis molding 416 to preventoverloading the force sensor 526. Since the cartridge itself providesthe face against which the pre-load spring pushes, the boot iseliminated and the cartridge couples directly with the force sensor.

As the cartridge is no longer constrained to a single diameter along itsfull length, its central section can be wider and accommodate a muchlarger ink reservoir 710.

The currently proposed pen design has an internal chassis 416 and anexternal tube molding 466. The external molding 466 is user replaceable,allowing the user to customise the pen 400. Removing the externalmolding 466 also provides the user with access to the pen's productlabel 652 (see FIG. 47). Skilled workers in this field will appreciatethat the chassis molding 416 and the base molding 528 could be modifiedto provide the user with access to a replaceable battery.

Referring again to FIG. 34, removing the external molding 466 (notshown) can also provide the user with access to the top-loading pencartridge 414. Once the external molding is removed, most of the lengthof the pen cartridge 414 is exposed. The user removes the cartridge bysliding it forwards against the pre-load spring 700 to extract its tail718 from the force sensor aperture 720, then tilting it upwards to freethe tail 718 from the cartridge cavity 722, and finally withdrawing thecartridge 710 from the pre-load spring 700 and cavity 722. The userinserts a new cartridge by following the same procedure in reverse.

Since a top-loading cartridge can have a much greater capacity than afront-loading cartridge, it is not unreasonable to require the user toremove the external molding 466 to replace the cartridge 414, since theuser will have to replace a top-loading cartridge much less often than afront-loading cartridge.

Referring to FIG. 35, the pre-load spring 700 can be provided with itsown cavity 716 and retaining ring 714 to make it easier to insert thecartridge 414.

Cap Assembly

The pen cap assembly 472 consists of four moldings as shown in FIG. 25.These moldings combine to produce a pen cap which can be stowed on thetop end of the pen 456 during operation. When capped, it provides aswitch to the electronics to signal the capped state (described in ‘CapDetection Circuit’ section below). A conductive elastomeric molding 522inside the cap 410 functions as the cap switch when it connects theinner 512 and outer 514 metal tubes to short circuit them (see FIG. 26).The conductive elastomeric molding 522 is pushed into a base recess inthe cap molding 410. It is held captive by the clip molding 544 which isoffered into the cap and snaps in place. A metallised trim molding 546snaps onto the cap molding 410 to complete the assembly 472.

The cap molding 410 is line-of-draw and has an aquagraphic print appliedto it. The trim 546 can be metallised in reflective silver or gold typefinishes as well as coloured plastics if required.

Pen Feedback Systems—Vibratory

The pen 400 has two sensory feedback systems. The first system ishaptic, in the form of a vibration motor 446. In most instances this isthe primary user feedback system as it is in direct contact with theusers hand 408 and the ‘shaking’ can be instantly felt and not ignoredor missed.

Pen Feedback Systems—Visual

The second system is a visual indication in the form of an indicatorwindow 412 in the tube molding 466 on the top apex 420 of the pen 400.This window aligns with a light pipe 448 in the chassis molding 416,which transmits light from red and green indicator LEDs 452 on the mainPCB 422. The indicator window 412 is positioned so that it is notcovered by the user's hand 408 and it is also unobstructed when the cap410 is stowed on the top end 456 of the pen.

Optical Design

The pen incorporates a fixed-focus narrowband infrared imaging system.It utilises a camera with a short exposure time, small aperture, andbright synchronised illumination to capture sharp images unaffected bydefocus blur or motion blur. TABLE 5 Optical SpecificationsMagnification −0.225 Focal length of lens 6.0 mm Viewing distance 30.5mm Total track length 41.0 mm Aperture diameter 0.8 mm Depth of field+/−6.5 mm⁷ Exposure time 200 us Wavelength 810 nm⁸ Image sensor size 140× 140 pixels Pixel size 10 um Pitch range⁹ −15 to +45 deg Roll range −30to +30 deg Yaw range 0 to 360 deg Minimum sampling 2.25 pixels per ratemacrodot Maximum pen velocity 0.5 m/s⁷Allowing 70 um blur radius⁸Illumination and filter⁹Pitch, roll and yaw are relative to the axis of the pen.Pen Optics and Design Overview

Cross sections showing the pen optics are provided in FIGS. 27A and 27B.An image of the Netpage tags printed on a surface 548 adjacent to thenib 418 is focused by a lens 488 onto the active region of an imagesensor 490. A small aperture 494 ensures the available depth of fieldaccommodates the required pitch and roll ranges of the pen 400.

First and second LEDs 434 and 436 brightly illuminate the surface 549within the field of view 430. The spectral emission peak of the LEDs ismatched to the spectral absorption peak of the infrared ink used toprint Netpage tags to maximise contrast in captured images of tags. Thebrightness of the LEDs is matched to the small aperture size and shortexposure time required to minimise defocus and motion blur.

A longpass IR filter 432 suppresses the response of the image sensor 490to any coloured graphics or text spatially coincident with imaged tagsand any ambient illumination below the cut-off wavelength of the filter432. The transmission of the filter 432 is matched to the spectralabsorption peak of the infrared ink to maximise contrast in capturedimages of tags. The filter also acts as a robust physical window,preventing contaminants from entering the optical assembly 470.

The Imaging System

A ray trace of the optic path is shown in FIG. 28. The image sensor 490is a CMOS image sensor with an active region of 140 pixels squared. Eachpixel is 10 μm squared, with a fill factor of 93%. Turning to FIG. 29,the lens 488 is shown in detail. The dimensions are:

-   -   D=3 mm    -   R1=3.593 mm    -   R2=15.0 mm    -   X=0.8246 mm    -   Y=1.0 mm    -   Z=0.25 mm

This gives a focal length of 6.15 mm and transfers the image from theobject plane (tagged surface 548) to the image plane (image sensor 490)with the correct sampling frequency to successfully decode all imagesover the specified pitch, roll and yaw ranges. The lens 488 is biconvex,with the most curved surface facing the image sensor. The minimumimaging field of view 430 required to guarantee acquisition of an entiretag has a diameter of 39.6s (s=spacing between macrodots in the tagpattern) allowing for arbitrary alignment between the surface coding andthe field of view. Given a macrodot spacing, s, of 143 μm, this gives arequired field of view of 5.7 mm.

The required paraxial magnification of the optical system is defined bythe minimum spatial sampling frequency of 2.25 pixels per macrodot forthe fully specified tilt range of the pen 400, for the image sensor 490of 10 μm pixels. Thus, the imaging system employs a paraxialmagnification of −0.225, the ratio of the diameter of the inverted image(1.28 mm) at the image sensor to the diameter of the field of view (5.7mm) at the object plane, on an image sensor 490 of minimum 128×128pixels. The image sensor 490 however is 140×140 pixels, in order toaccommodate manufacturing tolerances. This allows up to +/−120 μm (12pixels in each direction in the plane of the image sensor) ofmisalignment between the optical axis and the image sensor axis withoutlosing any of the information in the field of view.

The lens 488 is made from Poly-methyl-methacrylate (PMMA), typicallyused for injection moulded optical components. PMMA is scratchresistant, and has a refractive index of 1.49, with 90% transmission at810 nm. The lens is biconvex to assist moulding precision and features amounting surface to precisely mate the lens with the optical barrelmolding 492.

A 0.8 mm diameter aperture 494 is used to provide the depth of fieldrequirements of the design.

The specified tilt range of the pen is −15.0 to +45.0 degree pitch, witha roll range of −30.0 to +30.0 degrees. Tilting the pen through itsspecified range moves the tilted object plane up to 6.3 mm away from thefocal plane. The specified aperture thus provides a corresponding depthof field of +/−6.5 mm, with an acceptable blur radius at the imagesensor of 16 μm.

Due to the geometry of the pen design, the pen operates correctly over apitch range of −33.0 to +45.0 degrees. Referring to FIG. 30, the opticalaxis 550 is pitched 0.8 degrees away from the nib axis 552. The opticalaxis and the nib axis converge toward the paper surface 548. With thenib axis 552 perpendicular to the paper, the distance A between the edgeof the field of view 430 closest to the nib axis and the nib axis itselfis 1.2 mm.

The longpass IR filter 432 is made of CR-39, a lightweight thermosetplastic heavily resistant to abrasion and chemicals such as acetone.Because of these properties, the filter also serves as a window. Thefilter is 1.5 mm thick, with a refractive index of 1.50. Each filter maybe easily cut from a large sheet using a CO₂ laser cutter.

The Illumination System

The tagged surface 548 is illuminated by a pair of 3 mm diameter LEDs434 and 436. The LEDs emit 810 nm radiation with a divergence halfintensity, half angle of +1-15 degrees in a 35 nm spectral band (FWHM),each with a power of approximately 45 mW per steradian.

Pod Design and Assembly

TABLE 6 Pod Mechanical Specifications Size h63 × w43 × d46 mm Mass 50 gOperating −10˜+55 C. Temperature Operating Relative 10-90% HumidityStorage Temperature −20 to +60 C. worst case Storage Relative 5-95%Humidity Shock and Vibration Drop from 1 m onto a hard surface withoutdamage. Mechanical shock 600 G, 2.5 ms, 6 axis. ServiceabilityReplaceable jacket (part of customisation kit). No internal userserviceable parts - the case is not user openable. Power USB: 500 mA.External power adapter: 600 mA at 5.5 VDC.Pod Design

The pen 400 is supplied with a USB tethered pod, which provides power tothe pen and a Bluetooth transceiver for data transfer between the penand the pod. Referring to FIG. 31, the pod 450 is a modular design andis comprised of several line of draw moldings. The pod tower molding 554holds the pen at a 15 degree from vertical angle, which is bothergonomic from a pen stowing and extraction perspective, but also isinherently stable.

Pod Assembly

The assembly sequence for the pod 450 is as follows:

An elastomeric stop molding 556 is push fitted into the pod towermolding 554 to provide a positive stop for the pen when inserted intothe pod.

The pod tower molding 554 has two metal contacts 516 pushed ontolocation ribs under the stop. These contacts 516 protrude into a void558 where the nib molding 428 is seated as shown in FIG. 32. When a penis present, they contact the coaxial metal barrels 498 around the inkcartridge 414. These act as conductors to provide charge to the battery424.

The pod PCB 560 is offered up into the pod tower molding 554 and snappedinto place. Sprung charging contacts 562 on the metal contact piece 516align with power pads on the pod PCB 560 during assembly. The undersideof the pod PCB 450 includes several arrays of red, green and blue LEDs564 which indicate several charging states from empty to full. Blue isthe default ‘charging’ and ‘pod empty’ status color and they aretransmitted via a translucent elastomeric light pipe 566 as anilluminated arc around the pod base molding 568.

Despite a reasonable centre of gravity with a pen inserted, a castweight 570 sits in the base molding 568 to increase stability and lessenthe chance of the pod 450 falling over when knocked. The base molding568 screws into the tower molding 554 to hold the weight 570, light pipe566 and PCB 560 after the tethered USB/power cable 572 is connected tothe pod PCB 560.

Personalisation

In line with the market differentiation ability of the pen, the podincludes a pod jacket molding 468. This user removable molding isprinted with the same aquagrahic transfer pattern as the tube and capmoldings of the pen it is supplied with as a kit.

Therefore the pattern of the pen, cap and pod are three items thatstrongly identify an individual users pen and pod to avoid confusionwhere there are multiple products in the same environment. They alsoallow this product to become a personal statement for the user.

The pod jacket molding 468 can be supplied as an aftermarket accessoryin any number of patterns and images with the cap assembly 472 and thetube molding 466 as discussed earlier.

Electronics Design

TABLE 7 Electrical Specifications Processor ARM7 (Atmel AT91FR40162)running at 80 MHz with 256 kB SRAM and 2 MB flash memory Digital inkstorage  5 hours of writing capacity Bluetooth Compliance 1.2 USBCompliance 1.1 Battery standby time 12 hours (cap off), >4 weeks (capon) Battery writing time  4 hours of cursive writing (81% pen down,assuming easy offload of digital ink) Battery charging time 2 hoursBattery Life Typically 300 charging cycles or 2 years (whichever occursfirst) to 80% of initial capacity. Battery Capacity/Type ˜340 mAh at 3.7V, Lithium-ion Polymer (LiPo)Pen Electronics Block Diagram

FIG. 36 is a block diagram of the pen electronics. The electronicsdesign for the pen is based around five main sections. These are:

-   -   the main ARM7 microprocessor 574,    -   the image sensor and image processor 576,    -   the Bluetooth communications module 578,    -   the power management unit IC (PMU) 580 and    -   the force sensor microprocessor 582.        ARM7 Microprocessor

The pen uses an Atmel AT91FR40162 microprocessor (see Atmel, AT91 ARMThumb Microcontrollers—AT91FR40162 Preliminary,http://www.keil.com/dd/docs/datashts/atmel/at91fr40162.pdf) running at80 MHz. The AT91FR40162 incorporates an ARM7 microprocessor, 256 kBytesof on-chip single wait state SRAM and 2 MBytes of external flash memoryin a stack chip package.

This microprocessor 574 forms the core of the pen 400. Its dutiesinclude:

-   -   a setting up the Jupiter image sensor 584,    -   decoding images of Netpage coded impressions, with assistance        from the image processing features of the image sensor 584, for        inclusion in the digital ink stream along with force sensor data        received from the force sensor microprocessor 582,    -   setting up the power management IC (PMU) 580,    -   compressing and sending digital ink via the Bluetooth        communications module 578, and    -   programming the force sensor microprocessor 582.

The ARM7 microprocessor 574 runs from an 80 MHz oscillator. Itcommunicates with the Jupiter image sensor 576 using a UniversalSynchronous Receiver Transmitter (USRT) 586 with a 40 MHz clock. TheARM7 574 communicates with the Bluetooth module 578 using a UniversalAsynchronous Receiver Transmitter (UART) 588 running at 115.2 kbaud.Communications to the PMU 580 and the Force Sensor microProcessor (FSP)582 are performed using a Low Speed Serial bus (LSS) 590. The LSS isimplemented in software and uses two of the microprocessor's generalpurpose IOs.

The ARM7 microprocessor 574 is programmed via its JTAG port. This isdone when the microprocessor is on the main PCB 422 by probing bare pads592 (see FIG. 39) on the PCB.

Jupiter Image Sensor

The Jupiter Image Sensor 584 (see U.S. Ser. No. 10/778,056 (DocketNumber NPS047) listed in the cross referenced documents above) containsa monochrome sensor array, an analogue to digital converter (ADC), aframe store buffer, a simple image processor and a phase lock loop(PLL). In the pen, Jupiter uses the USRT's clock line and its internalPLL to generate all its clocking requirements. Images captured by thesensor array are stored in the frame store buffer. These images aredecoded by the ARM7 microprocessor 574 with help from the Callisto imageprocessor contained in Jupiter.

Jupiter controls the strobing of two infrared LEDs 434 and 436 at thesame time as its image array is exposed. One or other of these twoinfrared LEDs may be turned off while the image array is exposed toprevent specular reflection off the paper that can occur at certainangles.

Bluetooth Communications Module

The pen uses a CSR BlueCore4-External device (see CSR,BlueCore4-External Data Sheet rev c, 6-Sept.-2004) as the Bluetoothcontroller 578. It requires an external 8 Mbit flash memory device 594to hold its program code. The BlueCore4 meets the Bluetooth v1.2specification and is compliant to v0.9 of the Enhanced Data Rate (EDR)specification which allows communication at up to 3 Mbps.

A 2.45 GHz chip antenna 486 is used on the pen for the Bluetoothcommunications.

The BlueCore4 is capable of forming a UART to USB bridge. This is usedto allow USB communications via data/power socket 458 at the top of thepen 456.

Alternatives to Bluetooth include wireless LAN and PAN standards such asIEEE 802.11 (Wi-Fi) (see IEEE, 802.11 Wireless Local Area Networks,http://grouper.ieee.org/groups/802/11/index.html), IEEE 802.15 (seeIEEE, 802.15 Working Group for WPAN,http://grouper.ieee.org/groups/802/15/index.html), ZigBee (see ZigBeeAlliance, http://www.zigbee.org), and WirelessUSB Cypress (seeWirelessUSB LR 2.4-GHz DSSS Radio SoC,http://www.cypress.com/cfuploads/img/products/cywusb6935.pdf), as wellas mobile standards such as GSM (see GSM Association,http://www.gsmworld.com/index.shtml), GPRS/EDGE, GPRS Platform,http://www.gsmworld.com/technology/gprs/index.shtml), CDMA (see CDMADevelopment Group, http://www.cdg.org/, and Qualcomm,http://www.qualcomm.com), and UMTS (see 3rd Generation PartnershipProject (3GPP), http://www.3gpp.org).

Power Management Chip

The pen uses an Austria Microsystems AS3603 PMU 580 (see AustriaMicrosystems, AS3603 Multi-Standard Power Management Unit Data Sheetv2.0). The PMU is used for battery management, voltage generation, powerup reset generation and driving indicator LEDs and the vibrator motor.

The PMU 580 communicates with the ARM7 microprocessor 574 via the LSSbus 590.

The PMU uses one of two sources for charging the battery 424. These arethe power from the power and USB jack 458 at the top of the pen 456 (seeFIG. 15) and the power from the pod 450 via the two conductive tubes 498(see FIG. 24). The PMU charges the pen's lithium polymer battery 424using trickle current, constant current and constant voltage modes withlittle intervention required by the ARM7 microprocessor 574. The PMUalso includes a fuel gauge which is used by the ARM7 microprocessor todetermine how much battery capacity is left.

The PMU 580 generates the following separate voltages:

-   -   3.0V from an LDO for the ARM7 IO voltage and the Jupiter IO and        pixel voltages.    -   3.0V from an LDO for the force sensor and force sensor filter        and amplifier (3.0V for the force sensor microprocessor is        generated from an off chip LDO since the PMU contains no LDOs        that can be left powered on).    -   3.0V from an LDO for the BlueCore4 Bluetooth device.    -   1.8V from a buck converter for the ARM7 core voltage.    -   1.85V from an LDO for the Jupiter core voltage.    -   5.2V from a charge pump for the infrared LED drive voltage.

At power up or reset of the PMU, the ARM7 IO voltage and 1.8V corevoltage are available. The other voltage sources need to be powered onvia commands from the ARM7 574 via the LSS bus 590.

Indicator LEDs 444 and the vibrator motor 446 are driven from currentsink outputs of the PMU 580.

The PMU 580 can be put into ultra low power mode via a command over theLSS bus 590. This powers down all of its external voltage sources. Thepen enters this ultra low power mode when its cap assembly 472 is on.

When the cap 472 is removed or there is an RTC wake-up alarm, the PMU580 receives a power on signal 596 from the force sensor microprocessor582 and initiates a reset cycle. This holds the ARM7 microprocessor 574in a reset state until all voltages are stable. A reset cycle can alsobe initiated by the ARM7 574 via a LSS bus message or by a reset switch598 which is located at the top of the pen next to the USB and powerjack 458 (see FIG. 15).

Force Sensor Subsystem

The force sensor subsystem comprises a custom Hokuriku force sensor 500(based on Hokuriku, HFD-500 Force Sensor,http://www.hdk.co.jp/pdf/eng/e1381AA.pdf), an amplifier and low passfilter 600 implemented using op-amps and a force sensor microprocessor582.

The pen uses a Silicon Laboratories C8051F330 as the force sensormicroprocessor 582 (see Silicon Laboratories, C8051F330/1 MCU DataSheet, rev 1.1). The C8051F330 is an 8051 microprocessor with on chipflash memory, 10 bit ADC and 10 bit DAC. It contains an internal 24.5MHz oscillator and also uses an external 32.768 kHz tuning fork.

The Hokuriku force sensor 500 is a silicon piezoresistive bridge sensor.An op-amp stage 600 amplifies and low pass (anti-alias) filters theforce sensor output. This signal is then sampled by the force sensormicroprocessor 582 at 5 kHz.

Alternatives to piezoresistive force sensing include capacitive andinductive force sensing (see Wacom, “Variable capacity condenser andpointer”, U.S. Patent Application 20010038384, filed 8 Nov. 2001, andWacom, Technology, http://www.wacom-components.com/english/tech.asp).

The force sensor microprocessor 582 performs further (digital) filteringof the force signal and produces the force sensor values for the digitalink stream. A frame sync signal from the Jupiter image sensor 576 isused to trigger the generation of each force sample for the digital inkstream. The temperature is measured via the force sensormicroprocessor's 582 on chip temperature sensor and this is used tocompensate for the temperature dependence of the force sensor andamplifier. The offset of the force signal is dynamically controlled byinput of the microprocessor's DAC output into the amplifier stage 600.

The force sensor microprocessor 582 communicates with the ARM7microprocessor 574 via the LSS bus 590. There are two separate interruptlines from the force sensor microprocessor 582 to the ARM7microprocessor 574. One is used to indicate that a force sensor sampleis ready for reading and the other to indicate that a pen down/up eventhas occurred.

The force sensor microprocessor flash memory is programmed in-circuit bythe ARM7 microprocessor 574.

The force sensor microprocessor 582 also provides the real time clockfunctionality for the pen 400. The RTC function is performed in one ofthe microprocessor's counter timers and runs from the external 32.768kHz tuning fork. As a result, the force sensor microprocessor needs toremain on when the cap 472 is on and the ARM7 574 is powered down. Hencethe force sensor microprocessor 582 uses a low power LDO separate fromthe PMU 580 as its power source. The real time clock functionalityincludes an interrupt which can be programmed to power up the ARM7 574.

The cap switch 602 is monitored by the force sensor microprocessor 582.When the cap assembly 472 is taken off (or there is a real time clockinterrupt), the force sensor microprocessor 582 starts up the ARM7 572by initiating a power on and reset cycle in the PMU 580.

Pen Design

Electronics PCBs and Cables

There are two PCBs in the pen, the main PCB 422 (FIG. 39) and the flexPCB 496 (FIG. 19). The other separate components in the design are thebattery 424, the force sensor 500, the vibrator motor 446 and theconductive tubes 498 (FIG. 16) which function as the power connector tothe pod 450 (FIG. 31).

Main PCB

FIGS. 39 and 40 show top and bottom perspectives respectively of themain PCB 422. The main PCB 422 is a 4-layer FR4 1.0 mm thick PCB withminimum trace width and separation of 100 microns. Via specification is0.2 mm hole size in a 0.4 mm pad. The main PCB 422 is a rectangularboard with dimensions 105 mm×11 mm.

The major components which are soldered to the main PCB are the AtmelARM7 microprocessor 574, the AMS PMU 580, the Silicon Labs force sensormicroprocessor 582, the op-amps for force sensor conditioning amplifier600 and the CSR Bluetooth chip 578 and its flash memory 594, antenna 486and shielding can 612.

The force sensor 500, the vibrator motor 446 and the coaxial conductivetubes 498 use sprung contacts to connect to pads on the main PCB 422.All of these items are pushed down onto the main PCB 422 by the chassismolding 416 of the pen.

There are three connectors soldered onto the main PCB 422; the flex PCBconnector 612, the power and USB jack 458 at the top of the pen 456, andthe battery cable harness connector 616. The cable harness to thebattery is the only wired cable inside the pen.

Also soldered onto the main PCB 422 is the reset switch 598. This is inthe recess 464 shown in FIG. 5.

Flex PCB

The Jupiter image sensor 576 is mounted on the flex PCB 496 as shown inFIG. 19. As the critical positioning tolerance in the pen is between theoptics 426 and the image sensor 490, the flex PCB 496 allows the opticalbarrel molding 492 to be easily aligned to the image sensor 490. Byhaving a flexible connection between the image sensor and the main PCB422, the positioning tolerance of the main PCB is not critical for thecorrect alignment of the optics 426.

The image sensor 490, the two infrared LEDs 434 and 436, and fivediscrete bypass capacitors 502 are mounted onto the flex PCB 496. Theflex is a 2-layer polyimide PCB, nominally 75 microns thick. The PCB isspecified as flex on install only, as it is not required to move afterassembly of the pen. Stiffener 612 is placed behind the discretecomponents 502 and behind the image sensor 490 in order to keep thesesections of the PCB flat. Stiffener is also placed at the connectionpads 620 to make it the correct thickness for the connector 614 the mainPCB 422 (see FIG. 28). The PCB design has been optimised for panellayout during manufacture by keeping it roughly rectangular in overallshape.

The flex PCB 496 extends from the main PCB, widening around the imagesensor 490 and then has two arms 622 and 624 that travel alongside theoptical barrel 492 to the two infrared LEDs 434 and 436. These aresoldered directly onto the arms 622 and 624 of flex PCB. The totallength of the flex PCB is 41.5 mm and at its widest point it is 9.5 mm.

The image sensor 490 is mounted onto the flex PCB 496 using a chip onflex PCB (COF) approach. In this technology, the bare Jupiter die 628 isglued onto the flex PCB 496 and the pads on the die are wire-bonded ontotarget pads on the flex PCB. These target pads are located beside thedie. The wire-bonds are then encapsulated to prevent corrosion. Twonon-plated holes 626 in the flex PCB next to the die 628 are used toalign the PCB to the optical barrel 492. The optical barrel is thenglued in place to provide a seal around the image sensor 470. Thehorizontal positional tolerance between the centre of the optical pathand the centre of the imaging area on the Jupiter die 628 is +/−50microns. The vertical tolerance due to the thickness of the die, thethickness of the glue layer and the alignment of the optical barrel 492to the front of the flex PCB 496 is +/−5 microns. In order to fit in theconfined space at the front of the pen, the Jupiter die 628 is designedso that the pads required for connection in the Netpage pen are placeddown opposite sides of the die.

Pod and External Cables

There are three main functions that are required by the pod and externalcabling. They are:

-   -   provide a charging voltage so that the pen can recharge its        battery,    -   provide a relay mechanism for transferring stored digital ink to        the Netpage server via its Bluetooth/USB adapter and    -   provide a relay mechanism for downloading new program code to        the pen via its Bluetooth/USB adapter.        Pod

Again referring to FIGS. 31 and 32, when the pen 400 is inserted intothe pod 450, power is provided by way of two sprung contacts 516 in thepod which connect to the two coaxial conductive tubes 498 that hold theink cartridge tube 536 in the pen. The power for the pod 450 and the pen400 charging is provided by USB bus power.

The pod has a tethered cable 572 which ends in two connectors. One is aUSB “A” plug. The other is a 4-way jack socket. This 4-way jack socketis the same one present at the top of the pen (see socket 458 in FIG.15). When the 4-way jack is inserted into the pod's cable, it providespower for the pod and to the pen for charging. Otherwise, the power forthe pod and the pen charging is provided by the USB bus power.

Three indicator LEDs 452 are present in the pod. They indicate thestatus of pen charging and communications.

Pod PCB

The pod PCB 560 contains a CSR BlueCore4-External device. This is thesame type of Bluetooth device as used in the pen 400. The BlueCore4device functions as a USB to Bluetooth bridge.

Cabling

Three cables are provided with the pen. The first cable 572 is tetheredto the pod. At the other end of the cable is a USB A connector and a4-way jack socket. There are six wires going into the pod, the four USBwires and two from the 4-way jack socket.

The second cable is a USB cable 462 (FIG. 15) with a USB A connector onone end and a 4-way jack on the other end. The 4-way jack can beconnected to either the pod or the top of the pen.

The third cable is a plug pack power cable (not shown) which plugs intoa power outlet at one end and has a 4-way jack on the other end. This4-way jack can be connected to either the pod 450 or the top of the pen456.

Connection Options

FIG. 37 shows the main charging and connection options for the pen andpod:

-   -   Option 1 shows a USB connection from a host 630 to the pod 450.        The pen 400 is in the pod 450. The pod 450 and the pen 400        communicate via Bluetooth. The pod is powered by the USB bus        power. The pen is charged from the USB bus power. As a result        the maximum USB power of 500 mA must be available in order to        charge the pen.    -   Option 2 shows a USB connection from the host 630 to the pod 450        and a plug pack 632 attached to the pod cable 572. The pen 400        is in the pod 450. The pod and the pen communicate via        Bluetooth. The pod is powered by the plug pack. The pen is        charged from the plug pack power.    -   Option 3 shows a USB connection from the host 630 to the pod 450        and a plug pack 632 attached to the pen 400. The pen 400 is in        the pod 450. The pod and the pen communicate via Bluetooth. The        pod is powered by the USB bus power. The pen is charged from the        plug pack power.    -   Option 4 shows a plug pack 632 attached to the pod cable 572.        The pen 400 is in the pod 450. There is no communication        possible between the pod and the pen. The pod is powered by the        plug pack. The pen is charged from the plug pack power.    -   Option 5 shows a USB connection from the host 630 to the pen        400. The pen 400 is not in the pod 450. The host 630 and the pen        400 communicate via USB, allowing a wired, non-RF communication        link. The pen is charged from the USB bus power. As a result the        maximum USB power of 500 mA must be available in order to charge        the pen.    -   Option 6 shows the plug pack 632 attached to the pen 400. The        pen 400 is not in the pod 450. The pen is charged from the plug        pack power.    -   Other connection options are not shown. However, it should be        kept in mind that the pod is powered via its 4-way jack        connector (and not from the USB bus power) if there is a        connector in this jack. Also, the pen is powered from its 4-way        jack (and not from its pod connection) when there is a connector        in this jack.        Battery and Power Consumption

Referring to FIG. 44, the pen 400 contains a Lithium polymer battery 424with a nominal capacity of 340 mAh. It's dimensions are 90.5 mm long×12mm wide×4.5 mm thick.

Based on the pen design, Table 8 shows the current requirements forvarious pen and Bluetooth states. TABLE 8 Battery drain currents for allPen states. Total mA @ State Notes VBatt¹ Pen Capped Pen is off 0.110Pen Active Pen Down 92.7 Pen Hover-1 Pen up, trying to decoded tags 31.7Pen Hover-2 Pen up, decoding tags 62.9 Pen Idle Pen up, not trying todecode tags 28.8 Bluetooth Not Connected Bluetooth IC off 0.0 BluetoothConnection Bluetooth connected in low power, no digital ink 0.6 Timeoutto download Bluetooth Connected Bluetooth connected in low power Sniffstate 4.1 (Sniff) Bluetooth Connected Bluetooth connected in high powerActive state 50.1 (Active) Bluetooth Connecting Bluetooth trying toconnect Network Access 15.1 Point¹Sum of all current drains at battery. The Bluetooth currents can beconcurrent with and additive to the Pen-state currents.Pen Usage Scenarios

Some general usage scenarios are summarised here, showing the energyrequirements needed to fulfil these scenarios.

Worst Case Scenario

Summary: The pen is used intensively for 4 hours (cursive writing) andwill sit capped for one month (31 days), trying to offload storeddigital ink.

The energy requirement for this scenario is 968 mAh. The nominal 340 mAhhour battery would achieve 35% of energy requirement for this scenario.

Single Working Week Case Scenario

Summary: The pen is used for cursive writing for a total of one hour aday for five days and is capped for the remaining time. Total time forscenario is seven days.

The energy requirement for this scenario is 456 mAh. The nominal 340 mAhhour battery would achieve 75% of energy requirement for this scenario.

Single Working Week not Capped During Working Hours Case Scenario

Summary: The pen is used for cursive writing for a total of one hour aday for five days and is capped for the remaining time. Total time forscenario is seven days.

The energy requirement for this scenario is 1561mAh. The nominal 340 mAhhour battery would achieve 22% of energy requirement for this scenario.

Software Design

Netpage Pen Software Overview

The Netpage pen software comprises that software running onmicroprocessors in the Netpage pen 400 and Netpage pod 450.

The pen contains a number of microprocessors, as detailed in theElectronics Design section described above. The Netpage pen softwareincludes software running on the Atmel ARM7 CPU 574 (hereafter CPU), theForce Sensor microprocessor 582, and also software running in the VM onthe CSR BlueCore Bluetooth module 578 (hereafter pen BlueCore). Each ofthese processors has an associated flash memory which stores theprocessor specific software, together with settings and other persistentdata. The pen BlueCore 578 also runs firmware supplied by the modulemanufacturer, and this firmware is not considered a part of the Netpagepen software.

The pod 450 contains a CSR BlueCore Bluetooth module (hereafter podBlueCore). The Netpage pen software also includes software running inthe VM on the pod BlueCore.

As the Netpage pen 400 traverses a Netpage tagged surface 548, a streamof correlated position and force samples are produced (see NetpageOverview above). This stream is referred to as DInk. Note that DInk mayinclude samples with zero force (so called “Hover DInk”) produced whenthe Netpage pen is in proximity to, but not marking, a Netpage taggedsurface.

The CPU component of the Netpage pen software is responsible for DInkcapture, tag image processing and decoding (in conjunction with theJupiter image sensor 576), storage and offload management, hostcommunications, user feedback and software upgrade. It includes anoperating system (RTOS) and relevant hardware drivers. In addition, itprovides a manufacturing and maintenance mode for calibration,configuration or detailed (non-field) fault diagnosis. The Force Sensormicroprocessor 582 component of the Netpage pen software is responsiblefor filtering and preparing force samples for the main CPU. The penBlueCore VM software is responsible for bridging the CPU UART 588interface to USB when the pen is operating in tethered mode. The penBlueCore VM software is not used when the pen is operating in Bluetoothmode.

The pod BlueCore VM software is responsible for sensing when the pod 450is charging a pen 400, controlling the pod LEDs 452 appropriately, andcommunicating with the host PC via USB.

A more detailed description of the software modules is set out below.

The Netpage pen software is field upgradable, with the exception of theinitial boot loader. The field upgradable portion does include thesoftware running on the Force Sensor microprocessor 582. Softwareupgrades are delivered to the pen via its normal communicationmechanisms (Bluetooth or USB). After being received and validated, a newsoftware image will be installed on the next shutdown/startup cycle whenthe pen contains no DInk pending offload.

Netpage System Overview

The Netpage pen software is designed to operate in conjunction with alarger software system, comprising Netpage relays and Netpage servers.The following is a brief overview of these systems in relation to theNetpage pen—a detailed discussion of the software for these systems andthe specification of its interface to Netpage pen software is set out inthe cross referenced documents.

Netpage relays are responsible for receiving DInk from pens, andtransmitting that DInk to Netpage servers or local applications. Therelay is a trusted service running on a device trusted by the pen(paired in Bluetooth terminology). The relay provides wide areanetworking services, bridging the gap between the pen and DInk consumers(such as Netpage servers or other applications). The primary relaydevice will be a desktop/laptop computer equipped with a Netpage pod.Bluetooth equipped mobile phones and PDAs can also be used as relays.Relays provide the pen with access to WAN services by bridging theBluetooth connection to GPRS, WiFi or traditional wired LANs.

Netpage servers persist DInk permanently, and provide both applicationservices for DInk based applications (such as handwriting recognitionand form completion), and database functionality for persisted DInk(such as search, retrieval and reprinting).

Local applications may receive the DInk stream from the Netpage relayand use it for application specific purposes (such as for pointerreplacement in image creation/manipulation applications).

Internal Design

The Netpage pen software is divided into a number of major modules:

-   -   Image Processing    -   DInk storage and offload management    -   Host Communications    -   User Feedback    -   Power Management    -   Software Upgrade    -   Real Time Operating System    -   Hardware Drivers    -   Manufacturing and Maintenance mode    -   Force Sensor Microprocessor software    -   Pen BlueCore VM software    -   Pod BlueCore VM software

The remainder of this section gives a brief overview of these majorsoftware modules.

Image Processing

The position information in the DInk stream produced by traversing aNetpage tagged surface is produced by performing an analysis of taggedimages captured by the Jupiter Image Sensor 576.

The Image Processing module is responsible for analysing images capturedby Jupiter, identifying and decoding tags, estimating the pose of thepen, and combining this information to obtain position samples.

DInk Storage And Offload Management

Any DInk which corresponds to physical marking of a Netpage taggedsurface (e.g. excluding Hover DInk) must be reliably and transactionallyrecorded by the Netpage system to allow for accurate reproduction of theNetpage tagged surface. Ensuring such DInk is recorded is theresponsibility of the DInk storage and offload management software. Itpersists DInk in flash memory on the Netpage pen, and arranges foroffload of DInk to a Netpage server via a Netpage relay. This offloadprocess is transactional—the pen software maintains its record of DInkuntil it can guarantee that DInk has been received and persisted by aNetpage server.

DInk may be streamed in real time to applications requiring real timeresponse to DInk (for example applications which use the pen as areplacement for a mouse or table pointer, such as graphics editingapplications). This may be normal DInk or Hover DInk (for applicationssupporting hover), and the ability of the Netpage pen software to streamDInk to such applications is orthogonal to the storage and offloadrequirements for persistent DInk.

Host Communications

The Netpage pen software communicates with the Netpage relay eitherthrough wireless Bluetooth communication, or through a wired USBconnection. Bluetooth connectivity is provided by the pen BlueCore. USBconnectivity is provided by using the Bluetooth module in “pass through”mode.

The Communications module of the software is responsible for reliablytransmitting DInk from the DInk storage and offload management module tothe relay. It also provides management functionality such as maintaininga persistent list of known, trusted relays, and allows pairing withdevices according to user specification. The communications moduleincludes third party software (namely the ABCSP stack, see CSR, ABCSPOverview, AN11) provided by CSR for communication with the pen BlueCore.Bluetooth communication is only performed with Bluetooth paired devices,and uses the Bluetooth encryption facilities to secure thesecommunications.

User Feedback

The Netpage pen provides two LEDs (red and green) and a vibration motorfor user feedback. The user feedback software module is responsible forconverting signals from other software modules into user feedback usingthe provided mechanisms.

Power Management

The Netpage pen has a limited power budget, and its design allows fordynamic power saving in a number of ways. For example, the CPU candisable peripherals when they are not in use to save power, and the penBlueCore can be placed into a deep sleep mode or powered down when it isnot required. The CPU itself can be powered down when the pen is notperforming higher functions. Indeed, the only always-on components arethe Force Sensor microprocessor 582 and Power Management Chip 580 whichcan power on the CPU in response to external stimuli. The PowerManagement module 580 is responsible for analysing the current pen stateand optimizing the power usage by switching off un-needed peripheralsand other components as required. That is, this module intelligentlymanages the facilities offered by the Power Management module to provideoptimal power usage given the required pen functionality.

Software Upgrade

The Netpage pen software is field upgradable, obtaining new softwareimages via its Bluetooth or USB connections. The Software Upgrade moduleis responsible for managing the download of complete images via theCommunications module, validating these images against includedchecksums, and arranging for the pen to boot from a revised image whenit has been validated.

The Software Upgrade process happens largely concurrently with normalpen behaviour. The download of new images can happen concurrently withnormal pen operation and DInk offload. However, the actual switch toboot from a new software image is only performed when no outstandingDInk remains to be offloaded. This simplifies management of the internalDInk formats, allowing them to be upgraded as necessary in new softwareloads. Existing pairing arrangements with relays are expected to survivesoftware upgrade, although under some circumstances it may be necessaryto repeat pairing operations.

It should also be noted that small parts of the Netpage pen software,such as basic boot logic, are not field upgradable. These parts of thesoftware are minimal and tightly controlled.

Note that the Software Upgrade module also manages software images forthe Force Sensor microprocessor. Images for the latter form a part ofthe Netpage pen software load, and the Software Upgrade modulereprograms the Force Sensor microprocessor in the field when a new imagecontains revisions to the Force Sensor microprocessor software.

Real Time Operating System

The Netpage pen software includes a Real Time Operating System (RTOS)for efficient management of CPU resources. This allows optimal handlingof concurrent DInk capture, persistence, and offload despite thelatencies involved in image capture, flash manipulation, andcommunication resources.

The RTOS for the Netpage pen software is the uC/OS II RTOS from MicriumSystems (see Labrosse, J. L., MicroC OS II: The Real Time Kernel, 2ndEdition, CMP Books, ISBN 1578201039). This part of the Netpage pensoftware is comprised largely of third party code supplied by Micrium,tailored and customized for the needs of the pen.

Hardware Drivers

The Netpage pen software includes hardware drivers for all peripherals(both internal to the CPU and external to it) required for operation ofthe Netpage pen 400. This includes USRT 586, UART 588 and LSS 590drivers for external bus communication, as well as higher level driversfor managing the Jupiter Image Sensor 576, the pen BlueCore 578, theForce Sensor microprocessor 582, the Power Management IC 580, and otherinternal systems.

Manufacturing and Maintenance Mode

The Netpage pen 400 may be put into a special manufacturing andmaintenance mode for factory calibration or detailed non-field failureanalysis. A deployed pen will never enter manufacturing and maintenancemode. It is a configuration, diagnostic and rectification mode that isonly expected to be used by Silverbrook engineers under controlledconditions. The mechanism for placing the Netpage pen software intomaintenance mode is not described here.

Force Sensor Microprocessor Software

The Force Sensor microprocessor 582 is an independent CPU tasked withfiltering and resampling the force data obtained from the Force Sensor500 proper to produce a stream of force samples to be included into theDInk stream as recorded by the pen. It is also responsible forinitiating a wakeup of the CPU 574 in response to a pen down, uncap, ortimer event, in the case that the CPU has been switched off for powersaving purposes.

Pen BlueCore VM Software

The pen BlueCore is capable of running a small amount of software in avirtual machine (VM). Such VM software is highly resource limited, butcan access the Bluetooth functionality, the I/O ports, and a smallnumber of GPIO pins on the pen BlueCore. A small part of the Netpage pensoftware will run on the pen BlueCore in order to manage bridging theCPU UART to the USB connection provided by the pen BlueCore.

Pod BlueCore VM Software

The Netpage pod 450 contains a CSR BlueCore Bluetooth module, but nogeneral purpose microprocessor. The pod BlueCore runs Netpage pensoftware in its VM. This software is responsible for sensing when thepod 450 is charging a pen 400, controlling the pod LEDs 452 to indicatecharging and communications status, and managing the USB communicationlink between the pod BlueCore and the host PC. Note that BlueCoreprovides a split stack model for the Bluetooth network stack, and themajority of the Bluetooth network stack will in fact be running on thehost PC (where it has considerably greater access to resources).

Pen Assembly Sequence

The various sub-assemblies and components are manually inserted into thepen chassis molding 416 (see FIG. 41).

There are no special tools required to insert any of the assemblies asthere is extensive use of snap fits and bumps on moldings for location.The only assembly tool needed is a cold staking procedure required aftera testing to seal the pen assembly.

The assembly sequence for the pen is as follows:

Pen Chassis Assembly

The elastomeric end cap 460 is fed through an aperture 634 at the end ofthe chassis molding 416 and a tab 636 pulled through to secure it inplace.

Optics Assembly

The optics assembly sequence is as follows:

-   -   The lens is offered up to the aperture stop in the barrel and        adhered in place.    -   The infrared filter is pushed into place in the front of the        barrel molding.    -   The flex with image sensor is offered up to the top of the        barrel molding and accurately located onto two pins.    -   Epoxy is applied around the base of the barrel molding to bond        the flex into place and seal the image sensor from light and        particulate contaminants.        Optics Assembly Insertion

As shown in FIG. 42A, the optics assembly 470 with the unfolded flex PCB496 protruding is inserted into the chassis molding 416 and snapped intoplace. The IR LEDs 434 and 436 are then manipulated into cradles 638either side of the barrel molding 492 as shown in FIG. 42B.

Force Sensing Assembly Insertion

As shown in FIGS. 43A and 43B, the force sensing assembly 474 is fedthrough between the chassis molding 416 and the optical barrel molding492. The assembly 474 is pivoted down and the force sensor is secured inthe correct orientation into the chassis molding between ribs 640 and asupport detail 642.

The vibration motor 446 with elastomeric boot 644 is assembled into anaperture in the chassis 416. The boot 644 has negative draft on thesupport detail 642, which secures the motor 446 into the chassis 416 andorients it correctly.

A light pipe molding 448 is placed into the chassis molding 416 and is aforce fit.

PCB and Battery Insertion

The end of the optics flex PCB 496 is offered into the flex connector614 on the main PCB 422 and secured.

The main PCB 422 and LiPo battery 424 are then connected together as thesocket is on the upper side of the PCB 422 and is not accessible whenthe board is in the chassis molding 416. The battery 424 has foam padsto protect the components on the lower side of the PCB and to inhibitmovement of the battery when it is fully assembled.

Referring to FIG. 45, the main PCB 422 and battery 424 can now be swunginto place in the chassis molding 416, with care being taken not tounduly stress the flex PCB 496.

FIGS. 46A and 46B shows a cold stake tool 646 sealing a cold stake pin648 to an aperture 650 the base molding 528. The cold stake 648 is usedto help locate the PCB 422 into the chassis molding 416 and with gentlepressure the walls of the chassis 416 expand enough to allow snap fitsto engage with the PCB and hold it securely. The PCB can still beextracted by flexing the chassis walls in the same manner if necessary.The battery can be tacked in place with adhesive tape if required.

The base molding 528 is hinged onto the chassis molding 416 and is fullylocated when the cold stake 648 appears in the aperture 650.

Testing and Staking

At this point the assembly is complete enough to perform an optical andelectronic diagnostic test. If any problems occur, the assembly caneasily be stripped down again.

Once approved, a cold stake tool 646 is applied to the pin 648 from thechassis molding 416 swaging it over to hold the base molding 528 captive(FIG. 46B). This prevents any user access to internal parts.

Product Label

FIG. 47 shows a product label 652 being applied to the base molding 416,which covers the cold stake 648. This label carries all necessaryproduct information for this class of digital mobile product. It isexposed when the customisable tube molding 466 (see FIG. 49) is removedby the user.

Nib Molding Insertion

As shown in FIG. 48, the nib molding 428 is offered up to the penassembly and is permanently snapped into place against the chassis 416and the base moldings 528 to form a sealed pen unit.

Tube Molding Assembly

As shown in FIG. 49, the tube molding 466 is slid over the pen assembly.The tube 466 is a transparent molding drafted from the centre to allowfor thin walls. An aquagraphic print is applied to the surface with amask used to retain a window 412, which looks through to the light pipe448 in the pen during use. A location detail 656 on the chassis molding416 provides positive feedback when the molding is pushed home. The usercan remove the tube molding by holding the nib end and pulling withoutgaining access to the pen assembly.

Cap Insertion

The cap assembly is fitted onto the pen to complete the product as shownin FIG. 50.

Netpage Pen Major Power States

FIG. 51 shows the various power states that the pen can adopt, as wellas the pen functions during those power states.

Capped

In the Capped state 656, the Pen does not perform any capture cycles.

Corresponding Pen Bluetooth states are Connected, Connecting, ConnectionTimeout or Not Connected.

Hover1

In the Hover1 state 658, the Pen is performing very low frequencycapture cycles (of the order of 1 capture cycle per second). Eachcapture cycle is tested for a valid decode, which indicates that theuser is attempting to use the Pen in hover mode.

Valid Pen Bluetooth states are Connected or Connecting.

Hover2

In the Hover2 state 660, the Pen is performing capture cycles of a lowerfrequency than in the Active state 662 (of the order 50 capture cyclesper second). Each capture cycle is tested for a valid decode, whichindicates that the user is continuing to use the Pen in hover mode.After a certain number of failed decodes, the Pen is no longerconsidered to be in hover mode.

Valid Pen Bluetooth states are Connected or Connecting.

Idle

In the Idle state 664, the Pen is not performing any capture cycles,however, the Pen is active in as much as it is able to start the firstof a number of capture cycles within 5 ms of a pen down event.

Valid Pen Bluetooth states are Connected or Connecting.

Active

In the Active state 662, the Pen is performing capture cycles at fullrate (100 capture cycles per second).

Valid Pen Bluetooth states are Connected or Connecting.

Netpage Pen Bluetooth States

FIG. 52 shows Netpage Pen power states that are related to the Bluetoothwireless communications subsystem in order to respond to digital inkoffload requirements. Additionally, the Pen can accept connections fromdevices in order to establish a Bluetooth Pairing.

Each of the possible Pen Bluetooth related states are described in thefollowing sections.

Connected

In the Connected state 666 the primary task for the Pen is to offloadany digital ink that may be present within Pen storage, or to streamdigital ink as it is being captured. Whilst in the Connected state itshould also be possible for other devices to discover and connect to thepen for the purposes of Bluetooth Pairing.

In order to reduce power consumption whilst connected, it is desirableto take advantage of the relatively low bandwidth requirements ofdigital ink transmission and periodically enter a Bluetooth low powermode. A useful low power mode will typically be Sniff mode, wherein theperiodic Bluetooth activity required of the Pen is reduced based on theSniff interval, with the Sniff interval being determined by the currentbandwidth requirements of digital ink transmission.

Connecting

Whilst in the Connecting state 668, the Pen attempts to establish aconnection to one of a number of known NAPs (Network Access Points)either to offload digital ink stored within Pen memory, or inanticipation of a sequence of capture cycles.

Upon entry into the Connecting state 668, the Pen attempts anInquiry/Page of each device in round-robin fashion with a relativelyhigh frequency. If the connection is unsuccessful, the frequency ofInquiry/Page is reduced successively in a number of steps in order toreduce overall power consumption.

An Inquiry can last for 10.24s and is repeated at a random interval.Initially the Inquiry may be repeated on average at 5s intervals for thefirst 3 attempts, followed by 30s for the next 5 attempts and then 5minute intervals for the next 10 attempts and 10 minute invervals forsubsequent attempts.

Connection Timeout

In the Connection Timeout state 670, the Pen maintains the currentBluetooth connection by entering a Bluetooth low power Sniff state withrelatively long sniff interval (e.g. 2.56 seconds) for a period of atleast 2 minutes before disconnecting. Re-establishment of the connectionis not attempted, should the connection be dropped before 2 minutes haveelapsed.

Not Connected

In the Not Connected state 672, the Pen does not hold any digital ink inits internal memory, and is capped. There is no Bluetooth activity, andno Bluetooth connection exists.

Discoverable and not Discoverable

The Pen is only discoverable 674 during the major states of Hover1 658and Idle 664. The Pen periodically enters the inquiry scan and page scanstates whilst in Hover1 658 or Idle 664, in order to respond toconnection requests from other devices.

Cap Detection Circuit

Referring once again to FIG. 26, a cap detection circuit diagram isshown. As discussed above, the presence or absence of the cap assembly472 on the nib molding 428 can directly determine the Pen power stateand the Bluetooth state. The cap assembly 472 serves the dual purposesof protecting the nib 418 and the imaging optics 426 when the pen 400 isnot in use, and signalling, via its removal or replacement, the pen toleave or enter a power-preserving state.

As described in the ‘Pod Assembly’ section above, the pen 400 hascoaxial conductive tubes 498 that provide a set of externalcontacts—power contacts 678 and data contacts 680. These mate withcontacts 516 in the pod 450 to provide the pen with charging power and aUSB connection. When placed over the nib molding 428, the conductiveelastomeric molding 522 short-circuits the pen's power contacts 678 tosignal the presence of the cap.

The pen has three capping states:

-   -   cap on    -   cap off, not in pod    -   cap off, in pod

In the cap on state, the CAP_ON signal 682 is high. The pen will bepowered off, subject to other pending activities such as digital inkoffload, as described above in the NetPage Pen Bluetooth States section.

In the cap off not in pod state, the CAP_ON signal 682 is low. The penwill be powered on.

In the cap off, in pod state, the CAP_ON signal 682 is low. The pen willbe powered on.

The CAP_ON signal 682 triggers transitions to and from the Capped state656, as described in the NetPage Pen Power States section above, via thepower management unit 580 and the Amtel ARM7 microprocessor 574 (see PenDesign section above).

The battery charger can use the VCHG signal 684 to charge the battery.The VCHG signal 684 can be connected to the USB VBUS voltage (nominally5V) to allow the battery to be charged at up to 500 mA (based on the USBspecification). The VCHG signal can also be connected to a highervoltage generated by boosting the USB VBUS voltage (maximum chargingcurrent would be lower than 500 mA). Alternatively, the VCHG signal canbe connected to a different voltage, e.g. from a DC plug pack 632 (seeConnection Options section) connected to the pod 450. In this case, thepen is a self-powered USB device from the point of view of the USB host630.

When the cap assembly 472 is removed, the CAP_ON signal 682 is pulledlow via transistor Q1 686. The switching time of Q1, and hence thelatency of cap removal detection, is a function of the stray capacitanceof Q1 and the value of resistor R1 688. A value of 1 Mohm results in alatency of about 0.5 ms. The cap removal detection latency must bebalanced against the discharge rate of the battery in the capped state.A value of 1 Mohm yields a trivial discharge rate of 3 μA. Diode D1 690stops the battery being charged from the VCHG voltage 684 through R1688. The external USB host 630 (see FIG. 37) is connected to the USBdevice 692 in the pen 400 via the USB+694 and USB-696 signals. Althoughthe circuit in FIG. 26 is shown with reference to a four-wire USBinterface, the cap detection function of the circuit only relates to thetwo-wire power interface, and the pen can have a two-pin external powerinterface rather than a four-pin external USB interface depending onproduct configuration.

The above description is purely illustrative and the skilled worker inthis field will readily recognize many variations and modifications thatdo not depart from the spirit and scope of the broad inventive concept.

1. A stylus comprising: an elongate chassis molding; a nib at one end ofthe chassis molding; and, an elongate cover molding for close-fittingengagement with the chassis molding; such that, the cover molding isuser replaceable.
 2. A stylus according to claim 1 wherein the stylus isan electronic stylus and the chassis molding houses electroniccomponents.
 3. A stylus according to claim 1 wherein the cover moldingis a tubular molding that snap locks onto the chassis molding exterior.4. A stylus according to claim 3 wherein the tubular molding is slidinto place on the chassis molding, wherein the chassis molding has alocation detail to indicate that the tubular molding has been pushedhome.
 5. A stylus according to claim 3 wherein the tubular molding canbe slid off the chassis molding by grasping the nib end of the stylusand pulling the tubular molding off the opposing end.
 6. A stylusaccording to claim 1 wherein the cover molding is a suitable substratefor aquagraphic prints.
 7. A stylus according to claim 3 wherein thechassis has LEDs to indicate the operational status of the stylus andthe tubular molding has one or more transparent windows for viewing theLEDs.
 8. A stylus according to claim 1 wherein the elongate chassismolding has a substantially triangular cross section for pen-likemanipulation of the stylus.
 9. A stylus according to claim 2 furthercomprising an image sensor and lens for capturing images of coded datadisposed on a surface when the optical sensor is in an operativeposition relative to the surface; and a plurality of light sources forilluminating the coded data for the image sensor, the light sources eachconfigured for illuminating an area of the surface such that there is acommon region illuminated by all the light sources; wherein during use,at least one of the light sources is selectively extinguishable while atleast one of the light sources provides sufficient illumination forimage capture.
 10. A stylus according to claim 2 further comprisingelectrical contacts exposed by an opening in the chassis molding; and, acap that fits over one end of the chassis molding, the cap having aconductive portion positioned such that fitting the cap over said oneend of the chassis molding electrically connects the contacts to controlpower to the electronic components.
 11. A stylus according to claim 1further comprising an ink cartridge for insertion into the chassismolding, the ink cartridge comprising: an elongate body for containing asupply of ink, the elongate body having a nib end and an opposing end;and an engagement formation at the opposing end for engaging the nib endof another ink cartridge of the same type in the stylus in order toextract it from the chassis molding.
 12. A stylus according to claim 2wherein the chassis molding houses a rechargeable battery; and, astructure defining a receptacle for retaining an ink cartridge with aball point nib at one end, the structure having an open end for axiallyreceiving the ink cartridge as it is slid into the receptacle; wherein,the open end of the structure is at least partially formed by electricalcontacts configured for connection to complementary contacts within abattery recharger.
 13. A stylus according to claim 2 wherein one of theelectronic components is a force sensor comprising: a load bearingstructure for contact with an input member subject to a force to besensed; a sensor circuit for converting a force applied to the loadbearing structure into a signal indicative of the force; and, a pre-loadbias assembly for engaging the input member to bias it against the loadbearing structure.
 14. A stylus according to claim 9 wherein theplurality of light sources are two illumination sources mounted onopposite sides of the lens.
 15. A stylus according to claim 14 whereinthe two illumination sources have intersecting axes of illumination. 16.A stylus according to claim 15 wherein the optical sensor furthercomprises a control unit connected to the image sensor and the twoillumination sources such that the control unit extinguishes one of thetwo illumination sources upon detection of undesirable reflection fromthe surface.
 17. A stylus according to claim 16 wherein the control unitpredicts undesirable reflection from the surface using past detection ofthe undesirable reflection.
 18. A stylus according to claim 17 whereinthe control unit uses one or more captured images to compute theposition of the stylus relative to the surface in order to predict whenundesirable reflection will occur.